Earlier quoted context omitted.
I agree with most of this, but I'm curious about the specific case of Github. If I join a company, are there any big dangers to just having them add my personal GH account to their organizations or private repos, and then if I leave the company they can remove me again? This seems to be how a lot of developers in my orbit do things. (I mean any dangers at the account/permissions/privacy level - separate from "having…
No. Having a separate GitHub is just a pain. GitHub provides adequate separation itself (you can add multiple emails and configure notifications accordingly)
Personally, I like knowing that my personal GitHub credentials stay only on my personal devices and my work credentials stay only on my work devices. I never have to worry about the two mixing and any problems that might arise.