I guess like anything else its a debatable topic. If nothing else you'll have less algea. But if some parisites do decide to get past the qt then you didn't qt long enough. And if parisites do get into your main then the UV will not kill all of them. Only the free floating ones that go through the UV and hang long enough, not the ones on your fish(host), not the ones that fall to the substrate.
I veiw the UV as one of those not really necessary piece of mind type equipment. Ok for fish only or maybe Fowler, but definatly not a reef. Only for piece of mind
I really don't care for them, we have talked about them many times. Doing a search will yeild plenty to read on this board, and all much the same.
Thomas