Last week we analyzed games where it was wise to spend a whole tempo and play h2-h3 (or h7-h6 for Black) to avoid a very unpleasant pin. But sometimes it is a good idea to play such a move even if the pin is not our concern at all. In order to understand why we might want to prevent the Bg4 move anyway, we need to touch a strange chess phenomenon of Bc8. In many openings this poor guy frequently becomes a prisoner in its own camp, especially if Black plays e7-e6 as a part of his opening strategy. In such openings as the Queen's Gambit Declined (1.d4 d5 2.c4 e6) and especially the French Defense (1.e4 e6) Black's main goal is to activate Bc8. Also, there are a bunch of openings (like the Alekhine Defense, Gruenfeld Defense, Modern Benoni, etc.) where Black plays Bg4 and then captures the Nf3 as part of the fight for the central squares d4 and e5. So you shouldn't be surprised that one of White's main lines in the modern Benoni goes like this:
You might wonder why there is so much fight over the Bc8 development-- after all it is just one piece. But as GM Tarrasch pointed out about 100 years ago: "If one piece is badly placed, your whole game is bad." Is it an exaggeration? To some extent, yes. But as the Maestro himself proved in the next game, his rule has a very good point!
In the next game Mikhail Tal followed the strategic recipe of Dr. Tarrasch. First restrict the Bc8 and make Black's whole position passive. Then using the superior activity of your own pieces launch a King's Side attack. Finish the game with an elegant tactical blow! The game is especially impressive considering that the future World Champion was just 13 years old when he played it!!
In this game both sides pushed their 'h' pawns one square on the 5th move. Please note the difference between these moves. White's move 5.h3! sealed the fate of the Bc8, which was just a passive spectator of the coming massacre. Meanwhile, Black's move 5...h6 was pretty much pointless since White developed his Bishop anyway. His Bf4 was a pretty active piece, so Black eventually decided to offer a trade.
In the next game two big masters of positional play disputed the problem of the Bc8. Anatoly Karpov proved that he had learned Siegbert Tarrasch's lesson better:
To sum up, the h2-h3 move can have one or more of these ideas:
1) Prevent the dangerous Bg4 pin.
2) Restrict the Bc8.
3) Prepare the g2-g4 pawn storm.
It can also be just a useless waste of time (mostly in the games of beginners).
In conclusion, let me show you two games from the famous Karpov-Kasparov World Championship matches. Both games are incredibly complex and their analysis would go outside of our topic (if you are interested you can find excellent annotations by Kasparov in his books about the World Championship Matches vs. Anatoly Karpov). All you need to do is identify the ideas each player had when he played h2-h3!