I find this particular topic of interest because elimination is one of the more base needs within our collected instincts. Taking control over another's elimination is a straight route toward uncovering vulnerabilities. That being said, I think this is something that can be explored in many an erotic fashion.
Telling someone when and where they can go, pushing them to points of desperation or even making them go in rather unconventional ways are all methods for exploiting this vulnerability.
While I also enjoy more invasive play-catheters and enemas-I am also turned on by the idea of having someone shame themselves by going in their clothing on command. Perhaps drop your sub off four blocks from home, have them wet themselves and then leave them to a walk of shame through the neighborhood.
I also find diapers to play well into this control. Wearing and using them goes against everything that society, as well as instincts, tells us is acceptable. It adds considerably to the feelings of no control and helplessness through humiliation. By placing them upon someone and dictating if and when they can be removed, you are taking control of someone else's base functions and requiring that they rely upon you to alleviate their discomfort and restore their dignity.
Good stuff, great for the physical as well as the mental side of playing.