I don't usually sign contracts, when I do it's mostly NDAs. Often times the code has inherent competitive value. When not under an NDA, I'm well within my legal rights to reuse all of my code at any time, I could put everything I write on GitHub tomorrow with a GPL license and there wouldn't be anything stopping me legally (I would never do this, of course). When under an NDA but not granting exclusive usage rights, I'm not sure how that plays out, but I haven't ran into that situation yet. I'm in a very, very niche position.

I do appreciate the word of advice, and will make sure to look out for it when I do need to sign contracts for long-term work.