Read Only Profile Properties can be used to store additional data for a user that cannot be changed using the Active Social Edit Profile options.  A User Profile doesn't necessarily need to be limited to typical contact information.  A profile property could also be used to store other data related to the user that could be populated from an outside source.  Some examples include Active Directory Integration, External Membership Providers, E-commerce applications or Customer Relationship Management solutions. 

Any Profile Property can be marked as Read Only from the Members section in the Active Social control panel.  Read Only Profile Properties will be excluded from any Profile Edit screens within Active Social.