If my top has drained his balls and wants to keep fucking but is starting to get soft (various reasons, some of which I can't allude to in this forum) I can sometimes convince him to strap it on and continue fucking me. For me, it's about being totally dominated which means that my top has 100% permission to use whatever he wants on me.
I've also been with women who wanted to see what it was like to have a cock (plus it's basically the only way that a lot of them think they can dominate a man, so I love making them occasionally feel superior - and the only one who didn't want to try it with me of my 4 relationships was my ex-wife - there again, she is a Latina and the overwhelming consensus seems to be that they only ever feel the need to be subservient to men). I like to make EVERYONE'S time and experience pleasurable.