CCleaner is a PC optimizer tool from Piriform, that is simple to use and uses less system resources. Using this you can clean the temporary files which gets accumulated in your desktop or laptop. It also helps you to scan the registry and fix any error that might exist.
You would be amazed to see the amount of data that is stored by your browser even if you have selected the option to clear browsing data while exiting.
C-Cleaner also checks machine's temporary folder which is used by windows operating system (OS) to read or write data. Sometimes due to various reasons like sudden power off or application/OS crash, these files become unrecoverable by the operating system and sits on your machine. This result in reducing the size of machine's temporary folder. So less space means more time required by the OS to place new files in the folder and read from it.
One more area which leaves a lot of things on your machine is installing and uninstalling softwares. Not all software does a clean uninstall. Result, the registry contains entries which are left with no values inside them. Kind of one more empty room to check for the OS.
These factors lead to slowness of desktops and laptops over a period of time. I have been using C-Cleaner for very long time now and have found it useful. One could argue Tune-Up utility or System Mechanic softwares are better and/or have more features, but I am talking about a faster and easy to use tool and I found C-Cleaner to be a best option for me.
Latest C-Cleaner application comes with a menu on its right from where you can choose to clean the system (browser, applications etc) or clean the registry. It also gives you option to uninstall softwares that are installed in your machine. I have not used them much though.
One thing worth mentioning is that if you plan to clean your registry, its always advisable to take a backup of the same. CCleaner does not give you any option to blindly clean the registry as you can do it for the system clean option, which is good, because I do check manually the entries before deciding which one to remove. After all a little cross check will do no harm.