I didn't answer the poll because there aren't selections for
Only when I'm soaping up a female who had just laid eggs
Only when they get poop under their scales
If they ever had a really really bad shed, I'd soak them, but they never have bad sheds. They always come off in one piece. The beauty of racks!
Edit: Actually sorry, I guess I'll check "Whenever they need it" to go with my explanation...