This is rule for strategic chess with no tactics involved. This rule was good in days when players liked their pawn structures and didn't go too crazy with their moves. I think this is Nimzovich's rule from My System, but I'm not certain about this.
In my opinion, this rule should be taken very lightly today, as there is really a lot of examples, when players attack the "bad end" of a chain.
The reason is simple: Pawn is for 1, knight and bishop are for 3, rook for 5 and queen for 10. You should point your attention to place where you have advantage in total firepower. Pawns are very small part of that.
There is however higher probability that your pieces are aimed towards the "correct end" of a chain. That's reason why a lot of players respects this rule a lot. When you have bishops on d3 and c1 in closed french type position, you certainly want to play on a kingside.
In King's Indian it is very typical black plays c6 move even in some of the racing lines. On the other hand white sometimes play 0-0-0 with g4 h4 attack.
In french both black's f6 and white's a3 b4.
In e5 carocan white often pushes c4 and black takes some breathing space with f6.