I'd love to understand when a browser account/profile picker is useful? I do know that I need to pick e.g. account for which Gmail inbox I want to read, but that happens inside Gmail's account picker. I know that I could have profile in browser so that it always logins to right account, but then again when I browse different things, I do not want to constantly switch the browser profile either. Then on computers you have separate user accounts already that different family members can use without leaking their personal data.
For development, the incognito/guest is usually good enough (when you need to have "clean" state).