Pawn Push Post Castle

A friend of mine said that a highly ranked player he knows told him that after castling a player should immediately push the h (white) or a (black) pawn up a square to provide an escape hatch for the King. While I understand the idea, I have always thought that it depends on the prevailing board situation.  If my opponent is not in a position to threaten a back rank  attack, I'd rather not lose initiative (if I have it) or break up my pawn fortress.  Am I missing something?

Depends on the situation , if there are back rank threats then yes but other than that it seems like a loss of a tempo and creates a weakness . also which pawn you push can depend on the situation .