The only use case I could come up with is a dude that is actively trying to have a baby with one woman while at the same time is sleeping with one or more other women that he does not want to get pregnant. This assumes they figure out how to make this instant on/off.
The most obvious situation would be the woman are his wife and mistress. But there could also be poly situations that are open and honest but they would be an edge case at most.
