[wonnor]

Generally the advantage of a bishop over a knight is its increased mobility. The bishop pair is more mobile than N+N or B+N and can control both color complexes. To exploit the mobility advantage, good players tend to try to "open up" the position more to increase the scope of the bishops. A classic example of a strategic goal if you want to play for an open position is to keep the pawn structure fluid (as opposed to locked up), which can be too subtle for weaker players.