I am at a different pc, so I don't have the link, but there is actually scientific evidence regarding parasites and UV (which is *usually* what people recommend it for). IMO, THIS is where the UV gets dismissed by "experts" because there is just no evidence that it does much good. Certainly a UV will clear bacterial and algal blooms (and to my knowledge that is the largest application they are used for today). IMO, the UV, in this case, is the old "band-aid" analogy though. There is something fueling the growth of the bloom. Stop the fuel, stop the bloom.
Exactly. UV would be helpful in preventing parasites in tanks that share water. For a single tank, there is no evidence that it is beneficial for that purpose. I do use it on my outdoor pond, however, as a water clarifier.