The HomePage is the Portal Main Area.
All sub area hinerit from the main area. It is not possible to add a user and with rights from the main area.
However, it is possible to manage the rights of a Site Group.
In a sub area you can add user and provide them with very specifics rights. Without using a site group.
Adding a user to a subarea will automatically break the inheritance with his parent. You can also break inheritance from the area menu setting.
The rights added directly to a user in a sub area has precedence over all other types of rights. IE, Site Group the user is member of.