Your way over my head. I didn't realize that Chromebooks had anything to do with android phones.
I've never rooted... I've never had an android, but I did read about it a few years ago and it seems pretty straight forward. Basically you are just taking control of your phone (root access) and removing the carriers root control. It's really no different than sudo su on a linux machine, which is pretty much the equivalent of Administrator on a Windows system (well, actually System would be the actual equivalent access to root but Administrator is the super user ).
If I ever had an android, I don't know if I'd root it. I don't do anything fancy with my phones. I'm mostly looking for a device to make calls. I have heard that rooted devices get considerably better battery life.
Well, based upon what you've said, I'm guessing that you can update a rooted device all you want, but on a device tied down by the carrier, they quit pushing updates so as to force obsolescence. I don't think I like that... but then again, no one asked me.