I recently started wearing sun gloves when out fly-fishing. Here are my personal observations:
Sun protection. I suppose this has to be number one on the list. I started wearing them for this reason alone. I simply didn’t want my hands to look like my grandmother’s did, with large dark spots on the back, and with a leathery look, and regular little bleeding nicks. The gloves seem to do the job well, and considering that sun-cream washes off ones hands, the glove would be the way to go. We have harsh sun conditions here in South Africa, and one finds that particularly at high altitude, you very quickly burn.
Protection from wind and chapping. This was a surprise discovery. Regrettably I am an office person, and when exposed to wind and cold, my hands simply are not as tough as they need to be. I have found that the gloves help with this aspect of things.