In some cases, you do not know a user's account ID, but you want them to edit their user account. Having user/edit setup to edit the currently logged in user's account would help with sending users to the right edit page without needing to know their User ID. If not logged in, it would present them with the user login, and then shoot them to the edit page.
Places this might be helpful:
- Emails
- Help documentation to edit the user account
- etc