I agree that this activity is certainly in the area of edge play. I think in a pro Domme context it works best with a very experienced Domme who is also comfortable with the sub's maturity and level of experience.

As someone suggested earlier it is easy for some subs to get caught up in a fantasy and "bite off more than they can chew". That's why guardrails are important. Then, in the worst case scenario, the sub has an uncomfortable or unpleasant experience but suffers no real harm.

It's happened to me at least once but the only real consequence was a firm feeling of "Hell no, don't need to do that ever again!'

OTOH There have been times that while it was happening I was thinking "You idiot! What have to done?" yet within a few days or weeks I was tempted again.