odd0n3,
I think it's important to understand what Per Seat versus Per Server means according to Microsoft to answer your question.
Per Server is an easy one to understand and works best in a single server environment. If you have a file server you need at least as many CALs as maximum connections that will be made to the server at any one time. In otherwords, 15 clients in a Per Server Licensing mode requires at least 15 CALs if they will ever connect at the same time. The more servers you have the less likely this option will work for you as you'll need 30, 45, 60, etc licenses as the number of servers increases (assuming 15 clients).
Per Seat is more economical and reasonable in my opinion. If you have 5 servers and 20 clients you will only need 20 CALs to access all 5 of the servers. Add 5 more servers and you still only need 20 CALs to access the previous and the new servers.
Keep in mind that this is only in referrence to CALs not TS CALs or special Internet Connector CALs, or even the individual server and client licenses.
The only drawback to using Per Seat is that you will lose the license as mentioned in my previous post. Per Seat keeps the license with the server (it can accept as many concurrent connections as licenses). Per Seat distributes the licenses to the client (hence when you've had x number of clients connect over time equal the number of licenses you have there can be no more connections). This then relates to the previous post about losing licenses.