In a mutual zugzwang, an unneeded pawn move is a tempo in the bank; count both sides' spare moves and make sure you move last.
Take the sixth-rank zugzwang from lessons 4 and 5 (king d6, pawn e6 against king on d8/e8) and give each side a rook pawn far away: White a2, Black a6. The central structure is mutual zugzwang; whoever has to move his king there loses the fight. So the game is decided by the spare tempi on the a-file.