select the option to delete all but the most current system restore file. Some unneeded files will never be touched by the cleanup utility and you need to do so manually.
Whenever I run it I get an option to free 600MB + files.It's astounding,isn't it?
Right after deleting the files I had checked again running Disk Clean up option.Again it showed me 600 plus MB files to delete.
How could it be possible?
And on third attempt I got 2KB files to delete option.
All these attempts were made withing few seconds!!
Shall I delete all the dump files and error related files shown there?

Chowhound
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GameSpot
Giant Bomb
TechRepublic