Apparently, there are battles where both sides use more than one Pokemon.
'And even in these formats, it is useless due to lack of priorty, or fast users. (And yes, before you say anything, there is ONE very fragile Prankster Pokemon that can learn it.)
Plus, the way TC worded it suggests he already knows that its for doubles.
Anyway, to answer TC's question, In theory, you have a fast Pokemon who holds back a foe while a stronger foe delivers a killing blow. In practice, most things that learn it are two slow to make it worth a moveslot.