I just discussed this topic with a friend who also owns a gelding. She regularly checks on his sheath situation, but has never opted to clean it, as it rarely has any buildup at all, and, if it has, he seems to get rid of it naturally. Has never showed any discomfort and a bean has never been discovered either. This is a case when I agree - sheath cleaning would be unnecessary. She has owned the gelding for about 5 years now and he's dark pigmented down there, if it matters. My boy is also dark pigmented (with a couple of light patches), but normally I can scoop out a handful of smegma with one movement about once a month.
I have come a long way, to surrender my shadow to the shadow of my horse.