Unity requires you to sign up for an account in order to use it. As a consequence, your unity account could be terminated, severing your ability to work on your own projects as a result.

I know the Unity guys feel they're being reasonable and that it's a mainstream thing to require an account for a product, but I will never -ever- voluntarily lock my own personal projects inside someone elses system like that, and I think it's pretty galling of them to think they deserve that much control over my work.