It's strictly my personal preference. I've been able to prevent parasite outbreaks from spreading before the diseased fish can be captured and hospitalized. It's enabled me to treat copper-sensitive fish like puffers using UV and tank-transfer without the use of meds, copper or otherwise. I can now freely move fish from one tank to another with little to no acclimation for maintenance, population adjustments etc.
I have a lot of fish in my tanks, heavy bioloads and some significantly oversized filtration systems to support them. UV buys me time like nothing else, but mostly keeps me away from meds.
Interesting points, now I don't know what to do. My overall goal is a healthier reef, whichever one promotes a healthier reef is what I want. I could even go without the mandarin, I just wanted one since the tank would be filled with copepods anyways.