Autofill assumes all fields are associated with the person who is sitting at the computer. That assumption is wrong for an administrator editing user configuration. You don't want the admin's name or address by default if the admin is configuring a new user. Or if the admin role is editing blank user data. Admins are often managers so you can't just disable autocomplete at the browser level.
It's even worse for password fields. Browsers will aggressively attempt to fill the user's password into any password input, regardless of whether it's part of the site's login form or not. This works for most web sites, most of the time -- but it fails horribly for sites where the user really does need to enter a password for something else, like if you're setting a password on a wireless network or setting credentials on a new user you're creating.
