Nice and comfy . . . so long as you don't have a suit leak. Then, it is pretty worthless if the water is other than very warm. This is especially so if you will be in the water for a longer time.
I hate putting my 200 gram Thinsulate on here in the Summer, when I can bake in the 95 degree heat on the boat before getting into the water. However, I find that better than having to deal with a long deco in a flooded suit that provides no insulation--Thinsulate still provides insulation even when soaking wet (Thank goodness I have never flooded my suit . . . yet). Even when the water is 87 on the surface, I never get overheated once I am in the water.
Now, if you are talking about not wearing any underwear outside of the water, that is another matter altogether.