Why is he locked up?

LadyM suggested I turn this into a thread. I’ve just been secured while my key holder is away for a few nights. The main purpose of being locked up right now is to stop me from masturbating when she isn’t around. We still have sex regularly, and there’s no real denial involved in that regard. What are the reasons others get locked? I’m unsure how I’d handle actual denial or even cuckolding outside of fantasy scenarios. What do other couples do, and what kind of fantasies or wishes drive your decisions?