This is the software publisher's description.

Designed to clear unwanted and unnecessary files from your computer recovering valuable hard disk space and boosting your PC’s performance. While some files are necessary for your system to run properly others are useless and take up valuable hard drive space, jeopardizing your computer’s performance.

Windows applications create and place several temporary files on your computer. When an application terminates it should remove these obsolete/junk files but often times these files remain on your computer for various reasons such as program errors, sloppy architecture or improper system shutdown. Many applications also add folders and shortcuts to your Desktop and Start menu during their installation process.

This poses no real threat to your system but when you remove a program by deleting it in the program directory, these files are often overlooked. Most of these files are so small or hidden within your computer that you don’t even realize they are there. Though each of these files may be small, over time they can add up eventually stealing megabytes, sometimes gigabytes, of hard drive space and causing system errors. With Giant Disk Cleaner you can safely, easily and effectively remove these unwanted and unnecessary files from your computer. In addition, Giant Disk Cleaner provides other useful tool to help you easily and securely erase your files from your hard drive.