Applications
Invitation systems for websites are usually temporary. They are typically used for services in private beta testing, in order to control the number of users on the service. In other cases, they can be used due to limited availability of server resources. There are a growing number of sites which use invitation systems on a permanent basis to create exclusivity and to control quality of user-generated content. Rarely, they may be used on a permanent basis in order to aggregate social network statistics (all users will ultimately have a traceable connection to all others). They are sometimes used to avoid abusive types or spammers, by relying on mutual trust between all members.
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