It seems to me (and mostly just based on casual observation than anything else) that UV and ozone are used more on FOWLR systems. I've seen the occasional full on reef that employs them as well, but like with many things, they are just tools that we can choose to use or not and the usefulness will depend on what the user feels the benefits are versus the costs of doing so. A tank that has carbon will have clearer water quality than without, a tank with carbon and UV will be clearer than one with just one of those things, a tank with carbon, UV and ozone clearer still and so on. But then ozone and UV are things that need to be cleaned regularly, maintained and eventually replaced (UV lamps deteriorate and need replacing at the same schedule as any regular lighting for example). I've heard some say that they are detrimental to things like 'pods, but for the most part those guys cling to substrate anyhow and in event that they let go and go for a swim and get sucked in, then they'll be unlucky and probably get spat out of the UV as fish food but then again that was likely their fate anyhow, it just got sped up a little if anything.
So IMHO there is no real "right" or "wrong" but a million shades of grey in between.
They work for some situations, certainly not necessary in all situations.