Besides cleaning temporary files it also offers registry cleaner and various options for PC users like uninstalling programs, modfying startup programs list and also offers to delete system restore points created in your Computer.
Necessity of CCleaner
If you formatted your system and installed Windows freshly, the system performace looks much butter but as the days goes by regsitry entries related to program and temporary files may occupy big space in your hard drive so it recommended to user to run CCleaner at least once a day not only to protect your privacy but also to improve your system performace.
You don’t need to run CClenaer manually every time Widnows starts, you can set CCleaner to start at Windows Startup and delete all temporary files automtically.
For CCelaner to run automatically at Windows Startup
Open CCleaner click Options >Setttings and check or select Run CCleaner when the Computer starts.