Did a lot of random tests and it seems they don't use a few that should be pretty obvious, but maybe I just don't know wtf it thinks is close to another song. For example, pretty much any metal/hard rock to rap jump could probably save time by going through Body Count (Ice-T's "metal" band) but it never came up once unless I specifically requested it. Same with a band like Cypress Hill, which came up some but not as much as I'd expect. Or Anthrax, for that matter.