Depending on the relationship, NOT having it writing can be a liability. For pet and I, it confirmed the basis of trust that we have been building. We are watching out for each other, with an understanding of control and submission. It's actually working out very well for us.

One thing it did in a concrete manner was establish the priorities in her life. She had been struggling somewhat with how much power I should/would take, how it could mess up her job or family life if I pushed too hard and she submitted to somthing she shouldn't have. The contract gives her the two following items:
1) The responsibility to make her family #1, her job #2, and me #3. I'm not in this to get her fired or divorced. It's supposed to be fun.
2) The privelige (I'm not bothering with spell check, dang it!) to discuss her difficulties or confusion regarding any task or assignment without it coming over as complaining or making excuses. Sometimes her interpretation of what I want could get her in trouble, when what I was actually asking for was much more neutral.

Having this responsibilty and privelige make the relationship easier and more clear, leaving us room for more fun!

The agreement is also worded such that we may amend it under mutual agreement. The flexibility of the document is what keeps it alive. (I learned that lesson from the founding fathers of the gold ol' US of A! Just have a gander at the bill of rights, and the declaration!)