I've noticed that if I run CCleaner in safe mode more files are deleted. Can someone explain to me why this is? Also, is it advisable to run CCleaner in safe mode occasionally?

More stuff is deleted because the programs and/or services that are using/creating them don't run in safe mode therefore their logs and whatever else "junk" they produce aren't locked/in-use by Windows.

Just a couple of things that will be removed in safe mode that CCleaner never removes in normal mode are:
%windir%\pfirewall.log
%windir%\SchedLgU.Txt


Although I'm rarely in safe mode because it just too slow for me I do however make certain that I run CCleaner's Cleaner button. The Issues I don't touch in safe mode because it's given me some erroneous findings that it doesn't find in normal mode.

Thanks for that Andavari. One further question : Under Options > Advanced > Only delete files in Wind. temp. folders older than 48Hrs. Why is this? Is it best to keep this option checked ?

Btw, I'm sorry for the dumb questions, but hey, I've plenty more where these came from.

if you keep that checked, pages will load faster.
its mostly images and such and when you delete those, windows just puts them back on when you go back to a website.
if your just viewing the same pages and not surfing the web, i would leave this option checked.

Uh. No. Do research before you attempt to give an answer. It has nothing at all to do with loading webpages.

Only delete files in Windows Temp folders older than 48 hours - This will only remove files in the temp folder older than 48 hours

In other words, files found in the C:\Windows\Temp\ will be deleted only if they are 48 hours old or older. If you uncheck this option it will delete all files in C:\Windows\Temp\ regardless of age.

Woody, you can learn more about CCleaner in TwistedMetal's Beginners Guide.

Yes, I realize this. So what is the advantage, or otherwise, of having this option checked?

Well, a few advantages I can think of are you'll get a bit of extra space back by cleaning out those folders. Also, if you have a virus or malware that tends to hide in the temp files, you have better odds of it getting removed.