How do you decide when to play h6 (a6) over a less passive move?

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Samurai-X
 
 
[Example position]
 
Bg5 would be an annoying pin, but playing h6 delays development of the c8-Bishop, Queen, King, and Rooks. Decisions... decisions... decisions...

 

MrMojok

I wouldn't play it there, if I intended to castle behind it. And if you do play it there, he's just going to back the bishop off to h4. Then, are you going to follow up with g5?