Have you ever visited a page within Facebook where you signed up to enter a contest? More than likely, you were doing this within one of their applications developed by a third party.
One of the benefits of using these third party
applications is many of them, especially the larger companies that produce them, allow
you to incorporate different features into the applications, like “fan-gating”.
In addition, it also provides additional ways for your Facebook fan base to become more engaged with your Facebook page, create more brand awareness, and continue building those online relationships.
Read more about application in this article