Apples Safari browser is nothing but a pig. Its a resource hog and it doesn't clean up after itself. It even remembers every site you visit, even in porn mode......
What Safari does is records every site you visit and it doesn't matter if you have Private Browsing turned on or clear history.
This concerns many people.... Musician C. Harwick from Chapel Hill, NC did some snooping in Safari's hidden system folders. “With no good way of getting rid of them except manually (clearing the history doesn’t do it, and I don’t think resetting Safari does either), these hidden files are strewn all over the user’s hard drive unbeknownst to him waiting for snooping relatives (or more pertinently, law enforcement) to dig them up. I really like Safari, but I’m going to have to seriously consider using Firefox now (ack).”
Harwick discovered that Safari appeared to remember every site he visited in his history folder. It didn't matter what he set in his preferences. In a few months his history and top sites folders have grew to 100 mb.
He stated that the worst offender was the Quicklook folder.
Safari Is Fat Hog That Spies on You — Porn Mode Doesn’t Work | Cult of Mac