What @DMCS says is correct - there is an internal system at facebook that monitors user feedback - that means invites that users have declined, users that have blocked or hid your applications stories in their feeds, and possibly some sort of ratio between users that installed the application and removed it.
I was having trouble with these limits when I was developing the part of my application to do with user invites. After testing the application by sending requests and accepting declining them quite a bit, I noticed some limitations being enforced - before my application even went live!
That was when I learnt about
sandbox mode in the application settings panel. When an application is in
sandbox mode all the calculations and limitations are not enforced. Now you can go about testing your invitation systems without worrying about beeing deemed a "bad" application.
In addition only those users which you have granted access using the developers app role tab
(
https://developers.facebook.com/apps/YOUR_APP_ID/permissions )
will be able to see and use the application. Another thing to note is that invites sent from an application in
sandbox mode will not be received by users who have not been granted access.
