When you're screen sharing, you could receive company notifications that you don't want everyone.

Firstly, you don't necessarily coworkers to see some notifications. A manager might not want underlings to see their notifications, for instance, like that such and such is going to be laid off.

Secondly, who says the screencast is always for coworkers? You don't want a client or investor to see internal company notifications.

So, yes, there is a use case for suppressing notifications even if you have no personal logins.

Even fellow colleagues can send embarrassing notifications on work related accounts. "I can't believe they don't understand such a simple concept" is not something you want appearing in a message addressed to you from a co-worker.

I've seen my fair share of embarrassing messages show up from Microsoft Teams when someone else in my corporation is screen sharing.

^ This. I try to keep corporate device strictly corporate. No personal sign-in to any service.

I only have one computer, my work laptop and I use it for everything.

Some of those messages looked like they were from co-workers :P