hiberfil.sys should be the same size as the RAM (memory) in your computer,
and should not grow (unless you add more memory).
It will go away if you disable hibernation, and be recreated if you then
re-enable hibernation.
It is simply used to hold a copy of your computer's memory when it
hibernates - this is then reloaded into memory when Windows resumes.
Thus, the contents of hiberfil.sys are overwritten every time your machine
hibernates - there should be no need to delete/restart it.