When connecting to a network the process of finding the IP address is what ultimately allows you to connect. Now creating a router to router connection you are going to want your IP addresses to stay the same. Basically the difference in a static IP and a dynamic IP is that one IP stays the same and the other changes based off of a time limit. A static IP will always remain the same address. A dynamic IP will constantly change. This is beneficial because it slows attempts at unauthorized access to your network. In order for somebody to connect they will need to know the IP address at that current time. For connecting routers in a company there would be no need to implement a dynamic IP. The only IP that I would make dynamic is the default gateway. Reason being, is that it is an IP that you don't really need to connect to. It is basically a defense mechanism to prevent breaches. There are a lot of things you can do with your IP. For the most part your network is safe until you start allowing ports to to be accessed from the internet. One common use for forwarding ports is to setup or host a server. I recently did just that, I set up a server for a game and went through the steps of port forwarding and creating a static IP. Now these certain programs can be accessed from people I give the information to.