If a user is added to the Guests group (or the Domain Guests group, which belongs to the Guests group), when the user logs on, that user's profile information is only stored temporarily. When that user logs off, the entire profile is deleted. This includes everything stored in the %userprofile% directory: the user's registry hive information, custom desktop icons, and so on.

If the user is assigned membership to both the Guests group and the Administrators group, the user's profile will not be deleted when the user logs off. If the user is subsequently removed from the Administrators group and remains a member of the Guests group, the user's profile will be deleted the next time the user logs off. This is by design.

In the versions of Windows that are listed in this article, the Guests group plays a special role that integrates with the behavior of the Windows user profile scheme. Membership in the Guests group should only be granted to users who are intended to be guests on a computer or in a domain. It should never be granted to regular users. Guest accounts are not meant for users who have data and need to log on and off domains often. By intent, guests are people who may need to log to on a domain for a specific reason and then log off, but they do not stay or use the system for an extended time.

If users log on to a domain frequently enough that they would want to customize a desktop and keep data on it, they are not guests; they should be considered users, and should no longer be part of the Guests group.

Following this logic, if someone is made a member of the Administrators group, that user is definitely not a guest, which is why the user profile is not deleted when the user is a member of both groups.