I don't use it because it requires that I switch back. My wife won't be bothered to deal with learning the people-switcher (there's no reason she should, it's really her laptop in question), so using incognito means that once I close the window, it's clean again. It's a lot easier to remember to close the window than it is to remember to switch back to her account.

The option I finally chose to go with, is to install firefox on her computer as well. Firefox is for me, Chrome is for her. I'm an FF guy anyway. The main UX problem stands, though, it's too easy to be the wrong person.

I see you do UX at Google. Thank you for asking users questions like this (I really hope you were asking sincerely, not rhetorically). Please talk to users more.

I use the people switcher on computers I "control". It is convenient to have two accounts which stay logged in to various services. I do not like staying logged in, and might forget to log out of, computers that aren't mine.

Because that leaves your SO in the position of being able, even accidentally, to log in to your account.

Further, I'd guess that even if you absolutely trust your SO not to violate your privacy, you might still reasonably distrust the platform they're working on, and you might not want to expose your account credentials on a platform that you don't directly control.

I use people switcher on my laptop to switch between my two google accounts, but on my wife's laptop I see no reason to leave crumbs of my presence behind.

For me its easier to use a different browser. Chrome for her, Edge for me, Firefox for the kids.

The people switcher is a godsend for web dev work. I have one for my normal work window (email, ticketing, etc), and two for various types of test accounts. It's SO useful to not have to constantly log in and out. Thank you!