They're typically passwords that are only for testing accounts anyway, and that are known to the team members I'm sharing with.
But...it's easy to slip up now and then and forget you're actually putting in a password while screen sharing that it's probably best not to have your co-workers know! Obviously the worst is your actual O/S password, as knowing that could potentially allow a co-worker access to other passwords that are quite sensitive, but I'm not sure it's even possible to screen share your O/S login screen - probably shouldn't be! It is a good argument for not re-using that password for any browser-based logins, but SSO policies tend to make that impossible unfortunately. Mind you I use a pin for my O/S login screen, whereas for browser-based logins you can't.
