We old people use them to store our LPs in. The dairy companies (at least in Canada) eventually made them a bit smaller, so that vinyl records would no longer stack inside. Finding the old larger size at a yard sale or something used to be a big score.
Nowadays, our vinyl records and the milk crates they're stacked in gather dust in the corner. We download the albums from Napster and feel justified in that we do *own* the album, we just can't listen to it anymore, since the turntable is long since thrown away.