Why Worry over Bandwidth

We have a text application that runs on Sparc Solaris 2.4 and Online 7.11UC1. Users run it by telnetting from a pc into the Unix box (over a lan and wan) and it connects thru shared memory. We are in the process of convertting the app to client server. Now here is my question: when your telnetting, everytime a user (let's assume this user is going over the wan) hits a keystroke it goes over the wan, to the unix server and then back to the pc but in client server everything is local to the pc until the user saves or update a record (let's forget about queueries for now). So why are some people worried about bandwidth? I have the feeling I'm missing something so please tell me. thanks,