pagefile.sys? I takes up a lot of space on the main partition of my hard drive.
Pagefile.sys is your Windows virtual memory swap file. Its what windows uses when it runs out of physical memory. All in all it helps avoid out of memory errors.
Here is a link that addresses modifying/moving it.
I agree with the Dave M's comment as well. It is best to leave it alone and let windows manage it if unfamiliar with it. The first link deals with moving it, this link deals with deleting it (once again at your own risk).
Additionally to the other answer, pagefile.sys is also needed if you want to create a crash dump.