user11629: In the Sicilian Najdorf poisoned pawn variation what is the difference between including the moves 7...h6 8 Bh4 (as many top players do) and not including them?
[FEN ""]
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6. Bg5 e6 7. f4 Qb6 (7...h6 8. Bh4 Qb6 9. Qd2 Qxb2) 8. Qd2 Qxb2


user4588: According to the Game Database of ChessTempo, 7....Qb6 is actually more popular than 7....h6.
At the very top level, both moves have their supporters, e.g. Anand and Grischuk for 7....Qb6 and Vachier-Lagrave and Nepomniachtchi for 7....h6.
Both moves can easily transpose, as the main line of the Poisoned Pawn goes 7....Qb6 8.Qd2 Qxb2 9.Rb1 Qa3 10.e5 h6 11.Bh4.
After 7....Qb6, white has the option to play 8.Nb3, as mentioned by Seth-Riley. With the inclusion of 7....h6 8.Bh4, 9.Nb3 is not possible because of 9....Qe3+.
However, after 7....h6 8.Bh4 Qb6, white has the option to play 9.a3. If black takes the pawn with 9....Qxb2, white can trap the queen by 10.Na4. Instead black should continue his development, for instance with 9....Be7. Now white can play 10.Bf2, which is of course possible thanks to the inclusion of 7....h6 8.Bh4.


      [StartPly "13"]

      [FEN ""]
      1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Bg5 e6 7.f4 h6 (7...Qb6 8.Qd2 (8.Nb3) Qxb2 9.Rb1 Qa3 10.e5 h6 11.Bh4) 8.Bh4 Qb6 9.a3 (9.Nb3 Qe3+)(9.Qd2 Qxb2 10.Rb1 Qa3 11.e5) Be7 (9...Qxb2 10.Na4) 10.Bf2




user13044: One reason is that it avoids a certain line that you would get after playing 7...Qb6, which is 8.Nb3
If Black plays 7...h6 first, 8.Bh4 Qb6 9.Nb3 is no longer possible because Black can play 9...Qe3+ winning the f4-pawn. This would not have been the case in the  7...Qb6 line since the bishop would have still been on g5, protecting the pawn.
Another reason is that sometimes Black would like to play ...g5.
[FEN ""]
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6. Bg5 e6 7. f4 Qb6 (7...h6 8. Bh4 Qb6 9. Nb3 Qe3+ 10.Qe2 (10.Be2 Nxe4) 10...Qxf4) 8. Nb3 Be7 (8...Qe3+ 9.Qe2)


11629: <p>In the Sicilian Najdorf poisoned pawn variation what is the difference between including the moves 7...h6 8 Bh4 (as many top players do) and not including them?</p>

<pre><code>[FEN ""]
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6. Bg5 e6 7. f4 Qb6 (7...h6 8. Bh4 Qb6 9. Qd2 Qxb2) 8. Qd2 Qxb2
</code></pre>
 4588: <p>According to the <a href="http://chesstempo.com/game-database.html" rel="nofollow noreferrer">Game Database of ChessTempo</a>, 7....Qb6 is actually more popular than 7....h6.
At the very top level, both moves have their supporters, e.g. <a href="http://www.chessgames.com/perl/chessgame?gid=1721594" rel="nofollow noreferrer">Anand</a> and <a href="http://www.chessgames.com/perl/chessgame?gid=1784849" rel="nofollow noreferrer">Grischuk</a> for 7....Qb6 and <a href="http://www.chessgames.com/perl/chessgame?gid=1849673" rel="nofollow noreferrer">Vachier-Lagrave</a> and <a href="http://www.chessgames.com/perl/chessgame?gid=1859495" rel="nofollow noreferrer">Nepomniachtchi</a> for 7....h6.</p>

<p>Both moves can easily transpose, as the main line of the Poisoned Pawn goes 7....Qb6 8.Qd2 Qxb2 9.Rb1 Qa3 10.e5 h6 11.Bh4.</p>

<p>After 7....Qb6, white has the option to play 8.Nb3, as mentioned by Seth-Riley. With the inclusion of 7....h6 8.Bh4, 9.Nb3 is not possible because of 9....Qe3+.</p>

<p>However, after 7....h6 8.Bh4 Qb6, white has the option to play 9.a3. If black takes the pawn with 9....Qxb2, white can trap the queen by 10.Na4. Instead black should continue his development, for instance with 9....Be7. Now white can play 10.Bf2, which is of course possible thanks to the inclusion of 7....h6 8.Bh4.</p>

<pre>
<code>
      [StartPly "13"]

      [FEN ""]
      1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Bg5 e6 7.f4 h6 (7...Qb6 8.Qd2 (8.Nb3) Qxb2 9.Rb1 Qa3 10.e5 h6 11.Bh4) 8.Bh4 Qb6 9.a3 (9.Nb3 Qe3+)(9.Qd2 Qxb2 10.Rb1 Qa3 11.e5) Be7 (9...Qxb2 10.Na4) 10.Bf2

</code>
</pre>
 13044: <p>One reason is that it avoids a certain line that you would get after playing 7...Qb6, which is <strong>8.Nb3</strong></p>

<p>If Black plays 7...h6 first, 8.Bh4 Qb6 <strong>9.Nb3</strong> is no longer possible because Black can play <strong>9...Qe3+</strong> winning the f4-pawn. This would not have been the case in the  7...Qb6 line since the bishop would have still been on g5, protecting the pawn.</p>

<p>Another reason is that sometimes Black would like to play ...g5.</p>

<pre><code>[FEN ""]
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6. Bg5 e6 7. f4 Qb6 (7...h6 8. Bh4 Qb6 9. Nb3 Qe3+ 10.Qe2 (10.Be2 Nxe4) 10...Qxf4) 8. Nb3 Be7 (8...Qe3+ 9.Qe2)
</code></pre>
