There are multiple reasons why you may need to move or copy an SSL certificate from one web server to another. If you have purchased a wildcard certificate for your network, you are probably going to use that same certificate on a lot of different servers as it can be used to validate multiple websites and DNS names. Even if you are using singularly named certificates, you may be turning on multiple web servers to host the same site, to be set up in some sort of load balanced fashion. In this case, you will also need the same SSL certificate on each of the web servers, as they could all potentially be accepting traffic from clients.
When moving or copying a certificate from one server to another, there is definitely a right way and a wrong way to go about it. Let's spend a little bit of time copying a cert from one server to another so that you can become familiar with this task.