You can use mushclient.tlb inside Visual Basic to tell it the sorts of functions MUSHclient has built in.
To answer your question in more detail, can you tell me *where* you plan to put this code? Inside a script called by MUSHclient? Or starting a stand-alone VB program which then starts MUSHclient?
One of the functions supported by MUSHclient is world.GetWorld, which gives you an object to an existing world. This could be passed to a VB program which could manipulate that world. You can also use GetWorldList which gives you a list of the names of all open worlds, which you could then iterate through to (via GetWorld) to do things to each one.
As you have noticed, it wasn't really designed to create a new world from scratch, as world creation asks a couple of questions.
It seems to me from your question that you are trying to find a use for the file rather than solving a particular problem, but if you described the sort of thing you were trying to do, I could better suggest how to go about it, which may or may not involve using VB and the mushclient.tlb file. :)
The other answer would be that it is a useful reference, which shows what MUSHclient supports. You can also see this by visiting
http://www.mushclient.com/functions.htm