For sure your darksquare bishop is an active piece in the london system but h3 just prevents the exchange of the bishop against blacks knight with Nh5 but it doesn't avert the exchange after Bd6. Personally, I don't play h3 in the London System but I rather play the bishop back to g3. If black captures the bishop you get the open h-file and with the d3 bishop you can produce big pressure on blacks h7-pawn. This makes of course only sense if you haven't castled yet other wise you haven't an open file for your rook.
Furthermore the darksquared bishop is objectively your "bad" bishop and it shouldn't be that fatal to exchange it, especially against black darksquared bishop because it is his "good" bishop.
Finally I would say it depends on the kind how you play the london system. Do you try to win the game by initialising a direct kingside attack and mating your opponents king (than you should play without h3 and 0-0) or are you hoping for a better endgame with a solid centre pawn structure and a "good" against a "bad" bishop (than you should play 0-0 and h3 to prevent the exchange against blacks knight and the destruction of your pawn structure and exchange it against blacks dsb to hope for a better endgame because of your better minor piece).
If you want to play the London System seriously you should may get the book "Win with the London System" by Sverre Johnson: http://www.amazon.com/Win-London-System-Sverre-Johnsen/dp/1904600352/ref=sr_1_1?ie=UTF8&qid=1405030391&sr=8-1&keywords=winning+with+the+london+system
It helped me a lot to unterstand the main ideas behind the opening.
Hi all,
My first introduction to the London said that the DSB was key and showed h3 as a way to protect it at all cost but in other games I see it traded off readily.
So, my question is "what is the proper role of the DSB in this opening?"
Thanks, -B