Did not understand the purpose of INTERFACE entry in Access restrictions

Did not understand the purpose of INTERFACE entry in Access restrictions

hello,
I have been trying to get an understanding of the Interface entry in access restrictions.
i have tried to understand https://docs.safesquid.com/wiki/SafeSquid_Startup_Parameters and https://docs.safesquid.com/wiki/Access_restrictions these documents as well but could not get the hold of it. 
 if there is any simpler explanation which will explain the purpose and the expected output of the interface entry, please share it with me.