By default Windows 7 will use up space on your hard drive for its hibernation file, but if you never use sleep, and always turn your PC off, then this will never actually be used.
To disable hibernation and recover a little bit of hard drive space, launch REGEDIT, browse to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power, then set both HibernateEnabled and HiberFileSizePerfect to zero.