I wear a helmet and at least a jacket most of the time, but there are times when it's a nice day, traffic is nonexistent, and the pace is leisurely to just enjoy the experience of motorcycling without being closed up in a space suit. One time in particular was between Eau Claire and Lacrosse, WI. It was a Sunday, I had all the time in the world to get to Lacrosse, and I'd been riding in full gear for over a week and many thousands of miles and wanted a break. I might also do it on a ride to work, which is 1.5 miles with a 30 mph speed limit, especially if my hair is still wet from the shower.
The company health insurance does not pay for motorcycle accidents if the rider isn't wearing a helmet, so there is that to consider.