* Estoppel. Not going after someone when you are made aware of their violations may preclude you from ever being able to go after them.

* Severability. If one clause of your contract is unenforceable, the entire contract may become unenforceable unless you have a clause saying otherwise. (And even then, sometimes that won't apply!).

Taking the audience of HN as a reasonable sample of competent coders, I have seen more than a few commenters give very confident and very incorrect interpretations of the law. I am not so presumptuous to think that I am not in that class, although I do hope to do so more rarely than the average commenter.

And for what it's worth, I don't believe that the exaggerated premise I used was one that requires a lawyer to understand; it was merely an example that was so outrageous it would not be unreasonable for a lawyer to tell you that it was impossible for you to do what you want to do. An example that is not so outrageous is if you want to release something into the public domain--for there are jurisdictions where giving up all of your rights as an author is impossible.