Pawn chains define the strategy of many openings, the French Defense above all. Because pawns defend diagonally, an attack on the head of the chain achieves little; the proven plan is to undermine the base with a pawn break, since capturing the base collapses the support of everything above it.
The direction of the chain also tells each side where to play: you generally attack on the side where your chain points and where you have a space advantage. Understanding chains turns a confusing closed position into a clear plan — fix the chain, target its base, and open lines toward the wing where your pawns aim.