I'll start with the disclaimer that it is something each submissive would have to ask themselves at one point or other. I can only give my own perspective on this.

I have very few limits, the usual "no kids, animals, dead people, scat", I also have one or two which are phobias of mine, one of these is water bondage.
I have been in play and spacey when this activity was implied and I snapped right out of my spacey place and refused. I was pretty pissed at this guy for suggesting it knowing I had a fear of it and was never going to contemplate pushing it.

This was obviously an extreme one, and I would not react so badly if it were a soft limit of mine - for example - humiliation of certain sorts.

That is my two penneth, and it is up to each person within the dynamic to decide on such things.