I think that contracts are both good and bad. It should be fair for both parties. It should let you know the expectations. But some contracts will make you have to jump through too many hoops. No contracts can guarantee the health and temperament of the pup. Example:

Temperament and hip dysplasia can be influenced by the pups environment. It considered genetic but the environment plays its part. Is the dog too much running and jumping before it is mature enough. It bones are mature enough to handle the physical stress. The temperament is influenced by training, how the dog is raised. Improper handling of a dog will influence its temperament. Is the dog being properly socialized.

While contracts can be enforceable they can be challenging to enforce. I've had people try to give me a dog when I know that the breeder should have been given the dog back. I know dogs that have been bred but the dogs were sold with no breeding rights and under a spayed contract.