In Closed Sicilians, with White playing e4 and d3, the most desirable place for Black's dark-square bishop is the long a1-h8 diagonal, (where) it has great influence both on the centre and the queenside. John Emms, Starting Out: King's Indian Attack
In 1.e4 e5 openings, if you are forced to play the retreat ...Nf6-g8 early on in the game, it usually means that something has gone wrong. John Emms, Starting Out: The Scotch Game
Black reveals something about himself when he answers 1.e4 with a move other than 1...e5 or 1...c5. An Alekhine's specialist, for example, almost certainly likes positional imbalances and quick counterplay. He may have a problem with 1.e4 Nf6 2.Nc3!? because the Vienna Game (2...e5) is not likely to give him what he wants. Andrew Soltis, Transpo Tricks In Chess