A passed pawn is only useful if it is playing an active part in the game or if its owner has play elsewhere and intends to use it for endgame insurance. Most importantly, whoever controls the square directly in front of this pawn is doing well since that will either make the pawn mobile or immobile. For example, if White can control the e6-square (the square in front of the passer) then he will be able to push it whenever he feels it will help his cause. However, if Black controls this square then the passed pawn will be immobilized and may actually act as a shield for the enemy piece that rests there (thereby acting as a traitor to its own cause!).