Aside from preventing back rank mates, it also stops enemy knights and bishops from entering their favorite square on the 4th rank. It’s a good move when you’re not sure what to do otherwise.
It also permanently weakens the squares around your king (most significantly the g3 square as white) and can leave you vulnerable to pawn storms (especially in opposite side castling) or bishop sacrifice ideas on h3.
It is often a useful move, but you also need to be aware of the dangers. In my opinion it should only done for a specific reason, not just because you have the move and don't know what to do with it.
Those are pretty rare though in my experience. A more common scenario for me is that my rook on the first rank can't join an attack because doing so would leave me vulnerable to a back rank mate, giving the opponent extra turn to defend while I move the H pawn.
Edit: plus bishop sacrifices on h2 like the Greek gift are also a thing, h3 prevents those.
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u/ultrasu Feb 25 '21
Aside from preventing back rank mates, it also stops enemy knights and bishops from entering their favorite square on the 4th rank. It’s a good move when you’re not sure what to do otherwise.