The practice can vary significantly by the employer. Some employers prefer the usernames be new and unique to the employer, whereas others don't care. It's obvious that it's a major liability for the employee to reuse the username for personal and professional organizations.
Yeah, exactly. Personally I always thought that was a better policy (to have separate profiles) but I've actually had senior devs in the org tell me to just use my personal one and add my work email to it, so that's what I did. Seemed strange to me but I didn't question it too much. Maybe I should've, lol.