Keep prospects informed and part of the group
Likely participants on your Facebook page will be existing customers. They will ask you questions, they will sing your praises and they will even complain. Properly cultivated, this interaction can produce fans that will sell your products for you.
Get valuable feed back
Facebook is a real time connection with your real prospect. Companies have invested millions of dollars in focus groups and other research to find out what their customers want. On Facebook you can ask them and they will tell you.