You may need to allow access to the Internet only for a certain user/address group, whereas all other users should not be allowed to access this service.
This will be better understood through the following example (how to allow a user group to use SSH for access to servers in the Internet). Use the following rule to meet these requirements:
The rule will allow selected users (or a group of users/IP addresses, etc.) to access SSH servers in the Internet. The default rule (Block other traffic) blocks the other users and communication.