user15592: [FEN ""]
[STARTPLY "8"]

1. e4 e5 2. Nf3 d6 3. d4 Nc6 4. c3 Nf6 5. Bg5 h6 6. Bxf6 gxf6 7. Bb5 a6 8. Ba4 b5 9. Bb3 a5 10. O-O b4 11. a3 bxc3 12. Nxc3 exd4 13. Nxd4 Ne5 14. Re1 h5 15. h3 d5 16. Nxd5 f5 17. f3 Bc5 18. Ba4+ Bd7 19. Bxd7+ Qxd7 20. Nf6+ Kd8 21. Nxd7 Kxd7 22. Qc1 Bxd4+ 23. Kh2 Bf2 24. Rd1+ Ke7 25. Qxc7+ Ke6 26. Rd6# 1-0

I do not clearly understand the suggestion by Lichess computer analysis. What is the problem with the move 5.Bg5 if there is one ? Lichess computer analysis suggests me that 5.Bb5 was better, but my idea behind Bg5 was to defend e4 pawn and if you go for Bb5 you sacrifice the pawn and I do not see what compensation I have for it (I played for white). Thanks in advance. 

user12873: 5.Bg5 isn't that bad of a move, but it's not best because you have to give up your dark-squared bishop after 5...h6. Since some of your dark squares are weak (e.g., f4 and d4), keeping this bishop is necessary to defend the squares.
5.Bb5 is a better move because you're threatening to play 6.d5 and 6.dxe5 (these threats stop Black from taking on e4). If Black answers with 5...Bd7, you can go into this line: 6.d5 Ne7 7.Bxd7 Qxd7 8.Nbd2. Now you've got the e4-pawn protected, and have exchanged off your bad light-squared bishop for Black's good light-squared bishop.

user825: Both 5.Bb5 and 5.Bg5 are reasonable here. Lichess wasn't running multiple move analysis, but it didn't mean the move 5.Bg5 was bad.
5.Bb5 doesn't lose a pawn as 5...Nxe4 6.dxe5 dxe5 7.Qxd8+ Kxd8 8.Bxc6 bxc6 9.Nxe5 is better for White.

15592: <pre><code>[FEN ""]
[STARTPLY "8"]

1. e4 e5 2. Nf3 d6 3. d4 Nc6 4. c3 Nf6 5. Bg5 h6 6. Bxf6 gxf6 7. Bb5 a6 8. Ba4 b5 9. Bb3 a5 10. O-O b4 11. a3 bxc3 12. Nxc3 exd4 13. Nxd4 Ne5 14. Re1 h5 15. h3 d5 16. Nxd5 f5 17. f3 Bc5 18. Ba4+ Bd7 19. Bxd7+ Qxd7 20. Nf6+ Kd8 21. Nxd7 Kxd7 22. Qc1 Bxd4+ 23. Kh2 Bf2 24. Rd1+ Ke7 25. Qxc7+ Ke6 26. Rd6# 1-0
</code></pre>

<p>I do not clearly understand the suggestion by Lichess computer analysis. What is the problem with the move 5.Bg5 if there is one ? Lichess computer analysis suggests me that 5.Bb5 was better, but my idea behind Bg5 was to defend e4 pawn and if you go for Bb5 you sacrifice the pawn and I do not see what compensation I have for it (I played for white). Thanks in advance. </p>
 12873: <p>5.Bg5 isn't that bad of a move, but it's not best because you have to give up your dark-squared bishop after 5...h6. Since some of your dark squares are weak (e.g., f4 and d4), keeping this bishop is necessary to defend the squares.</p>

<p>5.Bb5 is a better move because you're threatening to play 6.d5 and 6.dxe5 (these threats stop Black from taking on e4). If Black answers with 5...Bd7, you can go into this line: 6.d5 Ne7 7.Bxd7 Qxd7 8.Nbd2. Now you've got the e4-pawn protected, and have exchanged off your bad light-squared bishop for Black's good light-squared bishop.</p>
 825: <p>Both 5.Bb5 and 5.Bg5 are reasonable here. Lichess wasn't running multiple move analysis, but it didn't mean the move 5.Bg5 was bad.</p>

<p>5.Bb5 doesn't lose a pawn as 5...Nxe4 6.dxe5 dxe5 7.Qxd8+ Kxd8 8.Bxc6 bxc6 9.Nxe5 is better for White.</p>
