If you’re looking for a quick way to clean out unused drive space, Windows 7 and on have a built-in tool called Cipher that can handle that easily. To wipe all free space on a drive (the C: drive in the below example) just use the following syntax:
cipher /w:c:There are a lot of additional features to this tool (which you can review at the link above), but a scheduled task to wipe your free space on a regular basis can greatly reduce the probability of data recovery in the event your device is stolen. Consider it a standard part of your regular hygiene along with drive encryption.
Hermit's Cave 