1. You only have one computer to access the Internet, so you can directly use this IP to access the external network without NAT (of course, if the broadband operator gives you a private IP, you will also access the Internet through the operator's NAT).

You have more than one computer to surf the Internet. You must use NAT to get all other computers online by installing wingate or segate or enabling Internet connection. Of course, you can also use the router to enjoy surfing the Internet (in fact, NAT is enabled).

Here to explain, the broadband operator of general home users will give you the account number and password of PPPOE to dial, which is actually similar to the above situation, except that the IP is automatically obtained and you don't need to set it manually.