I'm not computer expert, but I do know that hitting the Delete button doesn't really delete a file. Heck, anyone who watches Law and Order knows that! I think that what actually happens is that certain headers are stipped from the file, allowing it to be overwritten if and when it's necessary. Is this what constitutes "free space" on the hard drive? AND... does Ccleaner overwrite this area when asked to do so? How confident can a user be that deleted e-mails, Word files, etc. are not easily recoverable after executing a 'Wipe Free Space' command? Inquiring minds want to know. Thanks.
There's info about this on the relatively new Piriform Docs site. I've linked you to the relevant section.
http://docs.piriform.com/ccleaner/using-cc...free-disk-space
Hope that helps.