The thing to remember about contracts is that they're often only called upon when things go wrong. Most of the time everything runs smoothly, and whilst it might not be exactly what was agreed everyone is happy and willing to accommodate the variables. Unfortunately you can't predict in advance which ones will go wrong, so it's worth always having a contract even if you don't refer to it again. Whether this is a sheet of paper headed "Contract" or an exchange of emails doesn't matter. It also makes you look more professional, which in itself perhaps helps to ensure you won't get messed around.

Our contract specifies a minimum stage area, but we've turned up and been asked to play in some tiny spaces. So far we've never refused and we've worked with what we've been given - the important thing is that the contract gives us the right to refuse to play if we're really unhappy. However some things can't be overlooked. I've known a situation where the caller stopped the dancing halfway through the evening because he considered the floor was unsafe. If refusing to perform or curtailing a performance means the organiser loses money he may try to claim against the band unless you've given yourselves sufficient discretion.