Pawns are extremely useful in the game and are far more powerful than meets the eye. For instance, since pawns are the least valuable chess piece, they can be used to capture defended pieces. A single pawn approaching will force a more powerful piece, such as a rook or a knight, to retreat. A simple move of a pawn may reveal a hidden threat (see Discovered attacks). Also, when pawns are arranged in a diagonal line, with the frontmost pawns guarded by the pawns behind, they form an almost impenetrable wall capable of protecting any pieces directly behind them. A weak pawn structure, with unprotected, isolated pawns ahead of more valuable pieces, can be a decisive weakness. Furthermore, a pawn which has progressed all the way to the opposite side of the board may be promoted to any other piece except a king.
Read more about this topic: Chess Tactic