Hi em1500uk,
It really depends on how you use your PC.
Sometimes you may download some software and it ends up in these Temp files.
Many people have and don't realize they need to get this software somewhere safe.
There are first time users like I was that did not even know some of this software was there.
I "inherited" this computer and it was in terrible shape.
Some software was in Temporary Internet Files and never been moved out.
These files had never been "cleaned" even using Windows options.
So the first time cleaning was done by me using Windows options BANG.
What a big surprise!!! Blame it on the cleaner???
I think not!!!
The problem was due to inexperience not "stupidity".
This same thing happens to new users of CCleaner!!!
Luckily I had backed up these files before cleaning.I do have that much experience.
From what I have observed, keeping this box checked gives you time to move or copy what you need
before 48 hrs, are up.However,if you don't even know what is in there,48 hrs. later or more when you run CCleaner they will be deleted.
Personally,I leave this box checked. That way if I run CCleaner I still have time to "remember".
Everybody gets "tired" , "foggy" or what have you.
CCleaner has helped me safely get rid of these files and returned much memory and performance.
This computer had 3 yrs of junk slowing it down. What with power outages,system hangs,inexperience on how to get out of such "hangs" etc., Windows was still working!!!
Best Wishes,
davey