Only two scenarios I can think of:

1) You want to bid a specific trip(s) in a vacation month, but you can't do so with the block of vacation you have. "VACATION ANY" is the only way to break up (within a given bid month) a vacation block--used judiciously with PREFER OFF parameters, you would hope to get the exact days off you want, just not all together (and not blocking the trip(s) or other days you want to be able to work).

2) For the uber-junior, where it's a foregone conclusion to be hit with coverage over (say) Christmas: I've heard claims that VACATION ANY, combined with tactical trip bids, can get one some day(s) off over/near the actual holiday. It will NOT dodge the coverage monster; but, it may be a way to feed the beast better than would otherwise result (again, as in #1, because it "breaks up" the days and can give you a day(s) off where you might not get it with a SLIDE, due to coverage).