A new PC computer is pretty fast out of the box. As time goes on and files add up the seek time for the computer gets slower and slower. Duplicate files can take up space and freeing up this space gives more workability back to your PC and a bit more speed as well. Our family camera is shared among all of us. Its a high megapixel camera and every upload of the memory card is at least 1gigabyte of space. Things happen and duplicates in the multigig area are found. Here's eHow to find and deal with those duplicate files.
Tips & Warnings
don't delete something you need
softwares are only as good as the programmer. don't rely on them 100%. use your judgement in dealing with duplicates.
maybe backup your files prior to an external drive and then delete the backup after your cleanup job is found to be successful and no needed files are deleted by accident.