UV is good it you are addressing a specific problem, i.e. green water, bacteria, or parasites.
On the down side to UV if you using it address green water your not really addressing the problem, all the nutirants the algae aren't using (because you killing them) will still be in the water so will either cause an increase in algae on the plants etc or will just stay in the water which could cause other problems. IMO a better option is to identify the cause the of the nutirants and address that, for example increase the water changes, lower feeding, check your water change supply.
If you using it to address parsites or bacteria, this is fine in the short term but in the long term fish will loose their immunity, and when you change them to an other none UV tank you could have bigger problems. Generally if tank is well maintained and fish not stressed you shouldn't have problems with parasites or bacteria