user30189: I (black) reached this position in a game and realised that black's king would be totally exposed if white's bishop decided to take the pawn (1. Bxh6 gxh6).
Is the smart move here for white to sacrifice their bishop and to expose the opponent's king? Or since you can't see that far into the future, maybe it's just worth keeping your piece. What do you think?
[FEN "r2q1rk1/pp2b1p1/3p1nbp/1Np1p1B1/1nP1P3/6PN/PP2QPBP/R4RK1 w Qq - 0 1"]

1.Bxh6 gxh6


user15221: 
black's king would be totally exposed if white's bishop decided to take the pawn

Having little pawn cover and being "exposed" are completely different things. Black has five pieces available for the defense of their king, while White has only four pieces available to attack. One of those pieces is the bishop whose sacrifice you're evaluating, one of them is the fianchettoed bishop that, thanks to White's e pawn, has been deprived of the long diagonal and will take awhile to get into the action, one is a knight that has no available moves, and one is a queen, and while queens are more powerful than the other pieces, they're also much less disposable. With White's dark-squared bishop gone, taking out the h-pawn is going to be far from trivial.
While the sacrifice will result in two half-open files next to Black's kings, they're half-open on Black's side. That is, at least in the short run, removing the g pawn simply clears the file for Black's rooks! There's no way White's getting their rooks in a position to take advantage of the files (especially the g file) without a huge amount of work, and the h and e pawns are going to be major impediments to any pawn storm. If White can trade their bishop for the g and h pawns and have their g and h pawns be passed, that would be much more of concern.

user15223: This won't work. When you make aggressive piece sacrifices like this to expose the enemy king, you need to be able to follow up. In this case the obvious follow-up moves are Ng5 and Qh5, but both g5 and h5 are protected by Black's pieces. You could try f4, but it's slow - Black is not obliged to capture and after [pass] 2. f5 Bf7 you are once again out of attacking ideas.
For such an attack to work you need more firepower. For example, if you had the queen on d2 such that you can meet 1...gxh6 with 2. Qxh6, the sacrifice might work. Or maybe if somehow managed to trade light-squared bishops (trading one of your inactive pieces for an important defender of the opponent), and had the king on h1 with rooks on f1 and g1. As it is, Black's king simply has too many loyal bodyguards for your few attackers to break through.

user8300: The sacrifice makes very little sense here. A weakness is only a weakness if it can be exploited, and in this case white won't really have anything substantial to go on after giving up the bishop. But why can I be so certain that white won't have any good follow-ups, even if I don't consider all possibilities? What aspects of the position make it clear to me that white will not be able to exploit black's "vulnerable" king?
If we look a bit more concretely at the position after Bxh6, gxh6, what do we find? We find an entire army of black pieces, all of them ready to leap into the defense of their king! In particular, the knight on f6 and the bishop on g6 are at least as good as a pair of pawns when it comes to shielding black's king from direct attacks, so it doesn't really matter that black's pawn cover isn't that great. Also worth noting is the rook on f8, which can be placed on f7, providing even more defense for black's king.
While it's good that you're aware of the fact that one always has to be careful with allowing this kind of sacrifice around one's own king, this needs to be tempered somewhat. Ask yourself questions like "how will my opponent follow up their sacrifice?", "can the opponent easily open up lines of attack against my king?", "do I have enough defenders around my king?" etc. and you will find it a lot easier to correctly judge whether a piece sacrifice with the goal of initiating a king assault is likely to succeed.

30189: <p>I (black) reached this position in a game and realised that black's king would be totally exposed if white's bishop decided to take the pawn (1. Bxh6 gxh6).</p>
<p>Is the smart move here for white to sacrifice their bishop and to expose the opponent's king? Or since you can't see that far into the future, maybe it's just worth keeping your piece. What do you think?</p>
<pre><code>[FEN &quot;r2q1rk1/pp2b1p1/3p1nbp/1Np1p1B1/1nP1P3/6PN/PP2QPBP/R4RK1 w Qq - 0 1&quot;]

1.Bxh6 gxh6
</code></pre>
 15221: <blockquote>
<p>black's king would be totally exposed if white's bishop decided to take the pawn</p>
</blockquote>
<p>Having little pawn cover and being &quot;exposed&quot; are completely different things. Black has five pieces available for the defense of their king, while White has only four pieces available to attack. One of those pieces is the bishop whose sacrifice you're evaluating, one of them is the fianchettoed bishop that, thanks to White's e pawn, has been deprived of the long diagonal and will take awhile to get into the action, one is a knight that has no available moves, and one is a queen, and while queens are more powerful than the other pieces, they're also much less disposable. With White's dark-squared bishop gone, taking out the h-pawn is going to be far from trivial.</p>
<p>While the sacrifice will result in two half-open files next to Black's kings, they're half-open on Black's side. That is, at least in the short run, removing the g pawn simply clears the file for Black's rooks! There's no way White's getting their rooks in a position to take advantage of the files (especially the g file) without a huge amount of work, and the h and e pawns are going to be major impediments to any pawn storm. If White can trade their bishop for the g <em>and</em> h pawns and have their g and h pawns be passed, that would be much more of concern.</p>
 15223: <p>This won't work. When you make aggressive piece sacrifices like this to expose the enemy king, you need to be able to follow up. In this case the obvious follow-up moves are Ng5 and Qh5, but both g5 and h5 are protected by Black's pieces. You could try f4, but it's slow - Black is not obliged to capture and after [pass] 2. f5 Bf7 you are once again out of attacking ideas.</p>
<p>For such an attack to work you need more firepower. For example, if you had the queen on d2 such that you can meet 1...gxh6 with 2. Qxh6, the sacrifice might work. Or maybe if somehow managed to trade light-squared bishops (trading one of your inactive pieces for an important defender of the opponent), and had the king on h1 with rooks on f1 and g1. As it is, Black's king simply has too many loyal bodyguards for your few attackers to break through.</p>
 8300: <p>The sacrifice makes very little sense here. A weakness is only a weakness if it can be exploited, and in this case white won't really have anything substantial to go on after giving up the bishop. But why can I be so certain that white won't have any good follow-ups, even if I don't consider all possibilities? What aspects of the position make it clear to me that white will not be able to exploit black's &quot;vulnerable&quot; king?</p>
<p>If we look a bit more concretely at the position after Bxh6, gxh6, what do we find? We find an entire army of black pieces, all of them ready to leap into the defense of their king! In particular, the knight on f6 and the bishop on g6 are at least as good as a pair of pawns when it comes to shielding black's king from direct attacks, so it doesn't really matter that black's pawn cover isn't that great. Also worth noting is the rook on f8, which can be placed on f7, providing even more defense for black's king.</p>
<p>While it's good that you're aware of the fact that one always has to be careful with allowing this kind of sacrifice around one's own king, this needs to be tempered somewhat. Ask yourself questions like &quot;how will my opponent follow up their sacrifice?&quot;, &quot;can the opponent easily open up lines of attack against my king?&quot;, &quot;do I have enough defenders around my king?&quot; etc. and you will find it a lot easier to correctly judge whether a piece sacrifice with the goal of initiating a king assault is likely to succeed.</p>
