session files are state data and unrecoverable if deleted for the applications and should absolutely not default to be deleted for chrome, firefox, thunderbird.
My firefox session restore data for example can reprepesent days and weeks of work. Loosing it would be terrible. I thought I had removed the ccleaner setting before running it, but now I'm not so sure because later in the day I discovered both sesionrestore.js and sessionrestore.bak were missing for firefox. And I am really upset. But I'm not certain how it got deleted. Still, ccleaner shoudn't default to removing such precious information.
I agree completely. I've used CCleaner for years as a quick way to get rid of temp files, cache, and cookies. It frees up hard drive space and can fix a lot of browser performance problems. But I was bitten by this tonight--I didn't realize that getting rid of Saved Sessions was turned on by default. I lost about 20 tabs I was working on and now I have no way of knowing what they were. CCleaner is good at what it does, but stuff like this makes me reluctant to recommend it to friends who aren't techs.