A bad bishop is often a significant positional liability, especially in closed positions where pawn chains restrict its movement. The classic example is a light-squared bishop trapped behind pawns on e6, d5, and c4, where it has almost no useful squares and functions as little more than a tall pawn.
Improving a bad bishop is an important strategic skill. Options include placing the bishop outside the pawn chain before committing pawns to fixed squares, exchanging the bad bishop for the opponent's good bishop or a knight, or restructuring the pawns to open the bishop's diagonals.
The concept of good versus bad bishops is particularly important in endgames. A player with a bad bishop against a good bishop (or a knight) is often in serious trouble because the bad bishop cannot cover key squares. When evaluating trades, consider how the resulting pawn structure will affect your remaining bishop.