Very simple example :
zerg sees 2 rax opening he tells himself "terran might go for an early mm push to force me putting sunk, im just gonna drone up to have a good eco not making zergling" well too bad coze when terran gets out at 5min45 he has mm, 2 tanks and zerg has nothing to buy time or pick up reinforcements, terran pushes, GG. As simple as that.
As all timing push build order, you won't become world champion just doing that, but this is an easy way one time victory if you need it.