user24117: I only have about 35 games experience , so please excuse blunders.
I am in the following position. My app (dr wolf) wants me to capture on a3. However I fail to see either the extreme threat posed by the enemy Knight, or the extreme utility of the enemy vacating the b column, that would justify sacrifice (corr.: exchange) of my bishop.
[FEN "r1bqkbnr/ppp2ppp/2n5/4p3/3p4/N1PP1N2/PP1BPPPP/R2QKB1R b KQkq - 0 1"]

Can anyone explain the strengths of this move?

user2494: The thing about loosening White's pawn structure, specifically, is that Black is enabled to develop ...Qd8-e7 or ...Qd8-d6 as a threat, when White's replies a3-a4 or Qd1-c1 don't help White.
Good chess is a matter of introducing unused force with threats.

user20096: While some books give a slightly higher numeric value for the bishop than the knight, an exchange of bishop vs. knight is not regarded as a sacrifice. It depends on the exact position if a bishop or a knight is stronger. So this is simply an exchange.
Bxa3 makes the white pawn structure worse. White gets an isolated double pawn, which is bad news for white. Bxa3 also prevents the knight from Nc4, where it could put some pressure on e5. The negative: black gives away his bishop pair which is advantageous in a lot of positions (but not in all).
My engines (Leela chess zero and Stockfish) agree with Bxa3 but don’t agree with some other white moves. Don’t believe in engine moves, especially from weaker engines (or weaker preferences of strong engines).

user1090: Strong positives:

Damages white's pawn structure.
Paves the way for quick kingside castling.
Prevents Nc4, which would centralize the knight and attack e5.

Mild positives:

Removes a potentially "bad bishop" for a knight that is about to become strong.
c3 pawn loses a defender.
a3 pawn is attackable.

Mild negatives:

Opens b-file for your opponent's rook. :(
Trades a bishop for a knight (static material disadvantage of 0.5 pawns). :(


user19861: 
Black wrecks white's pawn structure

Black gains in development since he's trading an undeveloped piece for a developed one.

Although the center is sill fluid, black's dark square bishop is currently a "bad" bishop. in the short run, white's knight is the more active piece.

It removes the support of the c-pawn which opens up some tactical possibilities and also forces white to do something in the center rather than sitting back.



24117: <p>I only have about 35 games experience , so please excuse blunders.</p>
<p>I am in the following position. My app (<a href="https://apps.apple.com/at/app/learn-chess-with-dr-wolf/id1353041020?l=en" rel="nofollow noreferrer">dr wolf</a>) wants me to capture on a3. However I fail to see either the extreme threat posed by the enemy Knight, or the extreme utility of the enemy vacating the b column, that would justify sacrifice (corr.: exchange) of my bishop.</p>
<pre><code>[FEN &quot;r1bqkbnr/ppp2ppp/2n5/4p3/3p4/N1PP1N2/PP1BPPPP/R2QKB1R b KQkq - 0 1&quot;]
</code></pre>
<p>Can anyone explain the strengths of this move?</p>
 2494: <p>The thing about loosening White's pawn structure, specifically, is that Black is enabled to develop ...Qd8-e7 or ...Qd8-d6 as a threat, when White's replies a3-a4 or Qd1-c1 don't help White.</p>
<p>Good chess is a matter of introducing unused force with threats.</p>
 20096: <p>While some books give a slightly higher numeric value for the bishop than the knight, an exchange of bishop vs. knight is not regarded as a sacrifice. It depends on the exact position if a bishop or a knight is stronger. So this is simply an exchange.</p>
<p>Bxa3 makes the white pawn structure worse. White gets an isolated double pawn, which is bad news for white. Bxa3 also prevents the knight from Nc4, where it could put some pressure on e5. The negative: black gives away his bishop pair which is advantageous in a lot of positions (but not in all).</p>
<p>My engines (Leela chess zero and Stockfish) agree with Bxa3 but don’t agree with some other white moves. Don’t believe in engine moves, especially from weaker engines (or weaker preferences of strong engines).</p>
 1090: <p><strong>Strong positives:</strong></p>
<ol>
<li>Damages white's pawn structure.</li>
<li>Paves the way for quick kingside castling.</li>
<li>Prevents Nc4, which would centralize the knight and attack e5.</li>
</ol>
<p><strong>Mild positives:</strong></p>
<ol start="4">
<li>Removes a potentially &quot;bad bishop&quot; for a knight that is about to become strong.</li>
<li>c3 pawn loses a defender.</li>
<li>a3 pawn is attackable.</li>
</ol>
<p><strong>Mild negatives:</strong></p>
<ol start="7">
<li>Opens b-file for your opponent's rook. :(</li>
<li>Trades a bishop for a knight (static material disadvantage of 0.5 pawns). :(</li>
</ol>
 19861: <ol>
<li><p>Black wrecks white's pawn structure</p>
</li>
<li><p>Black gains in development since he's trading an undeveloped piece for a developed one.</p>
</li>
<li><p>Although the center is sill fluid, black's dark square bishop is currently a &quot;bad&quot; bishop. in the short run, white's knight is the more active piece.</p>
</li>
<li><p>It removes the support of the c-pawn which opens up some tactical possibilities and also forces white to do something in the center rather than sitting back.</p>
</li>
</ol>
