I too have a UV steriliser (my daughters bought it me for Christmas - excellent present).
I too noticed improved water clarity but I wanted one as a precautionary measure against excessive bacteria and parasites as I can't easily medicate my tank due to the mix of fish and shrimps. So far I have been pleased. One fish sustained an injury which started to get fungus but the fish fought it off without medication. Could be a coincidence but I believe the water condition is generally improved, particularly as the redox is improved by UV. I did read up about redox but all I can say is that it's good for fish. Very complicated chemistry stuff - not my strongest subject.
On balance, I would say UV can only bring good things to your tank but the choice of wattage and water flow will dictate how effective it will be.
Hope those ramblings are of some use.