for the love of new features, from my point of view having this option ON as DEFAULT is a bug - [discussed below]
I consider ccleaner an amazingly dumb-proof one-click tool for removing garbage from a computer.
For me the genius of CCleaner is that it NEVER deletes anything CRITICAL (unless told to, anyway)
When it deletes OLD (backed up) browser sessions - that's OK, that counts as privacy measure (most people will struggle to even find the files)
But when it deletes my WORKING DOCUMETS [ie web pages] just because i am not looking at them right now, that just feels wrong.