It is possible to transfer a user profile to a new user. This is useful when the role of a user is taken over by a new/different user. The history (of the old user) is preserved, and open items are automatically transferred to the new user.
To do this, click on the gear icon, then on 'Settings,' and then on the 'Users' tab. Click on the group of the user whose role you want to transfer. Then select the user to whom the role should be transferred. Check 'Yes, I want to transfer the profile.' Click 'Save.' The user profile has now been transferred, and the old user has been removed from the project.