Note too that updates may contain minor new features as well as bug fixes and security patches.
I just ran across one in Sierra.
When it was released, disabling Notifications left an empty space at the right hand end of my menu bar, and since I reinstalled, the Notifications icon fills the space; I had to boot into an old clone to make sure that I hadn't lost my mind.
More: And with luck, 10.13.4 will fix the Keychain Access bug that's kept me in Sierra.