While I agree that an agreement somewhat early on is important to protect and commit both sides I also believe that a little bit of exploration time is well spent before diving in too deep. Nothing worse than being committed to producing ten songs of a person who turns out to be a lot less talented than anticipated or someone who doesn't understand the (unwritten) laws of mutual respect and code of conduct between artist and producer/engineer.
I believe that it is important to clarify the mutual expectations of both the approach and the goals of the cooperation. Never (and I mean never) assume that the other party is familiar with business customs and working in studios. It is sometimes simple things like the use of drum machines, studio musicians, working hours etc. that make a project a living hell because people have very strong and very different opinions on how it should be done.
Then again, when set up correctly it can be a great and very fulfilling experience for both sides. I am currently enjoying one of those situations.
Just my 2 cents,
MisterBlue.