From a similar position in Silman’s Amateur’s Mind. Pawn moves are irreversible, and it’s important to weigh their short-term against their long-term effect. In the position below, Black has two bishops and White has a knight and a bishop. Black can drive the pesky knight away with the pawn move 1. … f5. However, he has to think whether the short-term result compensates for the negative long-term effect, because once he plays f5, opening the centre won’t be easy and the e5-square becomes weak. Since the bishops prefer an open centre and the knight outpost at e4 does not pose an immediate threat, the long-term implications of f5 speak against it. Instead, Black should play f6, preparing a pawn lever against the centre to secure the long-term advantage of his two bishops against bishop and knight.
Notes on Bishops and Knights: Drive Away the Piece or Open the Centre?