Invalid entries mean all kind of "marks" left in your PC's registry due to installation and un-installation of software applications, over a period of time. Such marks can lead to diminution of your PC's net productivity. Registry is one of the most important system software of your PC. While you are working on your PC the Windows automatially keeps on saving all relevant and path-related information in Windows registry. So the more you use your PC in terms of software applications, the larger is the number of invalid entries. In other words, with addition and removal of applications your Windows Registry will have more and more unnecessary data in the form of "Invalid Entries", which may lead to declines in PC performance.