There are two basic types of users on the LightRocket system: contributors and clients. Indeed you will see these two options on the registration page.
Contributors are users who will upload files into the system. Typically these would be photographers, staff members reporting from the field or indeed any individual who wishes to upload material to your archives.
Client users are those may wish to create and share lightboxes, download files from your system or simply browse content that may be restricted to users with accounts.
Client users could be members of your comms team, designers or media contacts.