As someone who is well versed in the BDSM lifestyle I feel it's necessary to say that a sub/Dom relationship is all about respect,trust and communication. Most practitioners would be horrified to have it put on a par with Non-Con, because BDSM is all about 'ultimate consent. Consenting for someone else to be responsible for your physical and emotional wellbeing. Which is why contracts are thoroughly discussed before.

For my part I had chosen a contract because he was so paranoid of doing anything p, he wouldn't even call me or take my hand without asking for express permission. It may have been endearing to start with, but to be asked your permission before every intimate moment sucks the romance and spontaneity out of of things very quickly. However he was convinced that If he so much as kissed me without asking me if it was allowed first I would run off to the police. So the contract was a way of giving him boundries to work within.
Obviously I still have the right to say no at anytime, but it still helped with trusting this wasn't some kind of set up or trap.