CCleaner works like using the recycle bin, except targeting specific file locations rather than you manually moving them to the recycle bin and deleting them. Thus all it really removes is the 'pointers' to those files from the MBR. The physical data is still there on your hard drive until it is overwritten, waiting to be overwritten. Software such as Recuva can scan for and recover this data that still has yet to be overwritten. The process to perma-delete data is a much more time-oriented task, which is why very few people do this by default. Safely Perma-deleting files is not just replacing all the 1s and 0s with 0s, because past 'x amount' of writes can be recovered by hard drive forensics. Programs such as Eraser allow you to overwrite deleted data with randomized 1s and zeros, even multiple passes of 1s and zeros in order to hide formerly deleted data.
I have my browsers set to automatically clear everything but form data in order to keep my browsers fast and functional while also automatically deleting most tracking cookies.