Unless you use hibernate facility this file is not of use. so you can
delete it!
but first to disable it, go to start=>control panel => power options =>
hibernate and remove the tick in 'enable hibernation' check box. this will
disable the hibernation support and will unlock the hiberfil.sys file and
later you can delete it.
even if you want to do defrag and have hibernation facility, you can disable
and delete it, then perform a defrag and once again enable it. by doing so,
the big chunk will be pushed to end of the drive and will not come
in-between the usage area
- Narayanan