I think this is really only something you're going to do if a) piles are lowering anyway, or at least one pile has already emptied and b) it looks like Provinces are going to be difficult to empty. This is most often the case in curser/looter games, but can also happen in engine games with a contested part. In these cases, you really have to be mindful of how much is left in each pile, and what your current score is. If you're losing, you want to keep the piles up to make it harder for your opponent to end the game in their favor.
Of course this is mainly about pile emptying. For pile lowering, I think the main card to look out for is Goons. With Goons, I'm perfectly happy grabbing a bunch of Pearl Divers, because they're basically cheaper Great Halls (or better, depending on how many Goons I have in play).
I dunno. Really, the strategy for pile lowering is the same as for pile emptying - you're looking for the same conditions, you're just starting earlier. In order for it work without a contested pile, you need some sort of +Buy or gainer.