I agree with EBGreen and Chris, but I want to add that you might want to consider testing your application against the newer versions of the framework and allow your application to run against those versions you deem to work well against (this can be done using some configuration trick, but unfortunately, I can't find reference to it). This way, your application could work against the version the client may already have installed.
I suggest this because:
- New framework versions may give you a performance boost.
- The client may already have another version installed on their computer and it would be a shame to, as you say, waste hard drive space.
- You may want to run your application against a newer framework version sometime in the future and if your client already has that version and is running the current version of the application, there won't be an old framework on their computer.
Still, I'm lacking some information you may have, such as the means of distribution, the profiling of clients' machines, etc.
