I've heard it before. Ain't gonna say where, when or under what circumstances, but I assure you that I wasn't one of the parties directly invovlved (shall we say?).

But if you float plastic wrap on top of paint it will prevent a skin from forming. Of course, it's much easier and neater just to replace the lid.

And you can do a close fit of plastic wrap over a container of opened ice cream and prevent ice crystals from forming.

Wait! It occurs to me that you might talking about plastique wrap. That too has its uses, one of which it to start very hot, very fast fires.