It's just so if that is set, then when you go to run, it will switch to that file before starting compilation. It's just a minor thing that would make my life easier because every time I am working in the support files and I have a few of them, and I *always* forget to switch to the main file.
It's just a little thing that irks me - nothing serious, but if it would be possible to add this, that would be great.
