Is it good to take a fianchettoed Bishop? I have faced this fairly often in quite a few openings, but there seems to be a theme with players putting their Bishop on a square like h6, supported by a queen and attacking the fianchettoed Bishop next to the castled King.
What are the ideas behind this? Is it something I should be bringing into my own gameplan and if so is taking the fianchettoed Bishop a good thing to do? It seems to me to be the only point in putting it there.
There are two reasons for doing this and immediately taking the fianchettoed bishop is not one of them:


Provoke Black into playing BxB when you hope to follow up with Ng5, drive the f6 knight away and then mate on h7 
Prevent black from playing h5 until you have been able to play h2-4-5 to pry open the
black king's position.


It can even be worth sacrificing the exchange with h5, Nxh5 Rxh5 to smash open the black citadel.