Maintain a list of members who can have special access to your system, or who wish to express an interest in your services.
Provide special access levels to users, to give them access to secure pages or data.
Provide opt in/out pages for your customers to join or leave your mailing list.
Provide questionaires to your members to complete, so that this information can be used to filter mailouts based on demographics.
Provide password protected pages and files that only authorised users can access.
Keep a repository of files belonging to invidual members, that only they can access. Perfect for storing excel spreadsheets, consultancy data, invoices etc.
Make some membership data public so that the general public can search and view it.
Import / Export data from offline contact databases.