Windows 7 page file usage

I wanted to know, whether paging in win7 occurs only when the physical memory is not enough for the current running processes, or if windows uses the page file in other cases as well.

At first I thought about disabling the page file, but that would only make sense, if the os actually uses paging even when there is still free RAM left, and therefore disabling it would make no sense.

Any kind of explanation or advice appreciated