What is a domain user? How is it different from a webuser?
A web user has access in this way mydomain/~username
A domain user has access in this way mydomain/
The domain user can access all of your web site's files. If you want to give someone a sub-website but not allow them to fiddle with your main site, make them a webuser. If you want them to be able to edit your entire site, make them a domain user.