You have to root the phone to login to your corporate Google account. If you don't want to login to your corporate account you don't have to root the phone. If your manager wants you to have a phone with corp access then he will get you a corporate phone to do it. However many would rather root their phone than have a separate phone for their private life so Google provides that option. If that starts being a legal problem for Google I'm pretty sure they will stop rooting phones and just require people to get corp phones instead.