1. you don't want your boss / parents to find out what websites / files you were watching
2. your harddisk has low free space
3. you are having  trouble opening / signing into some websites
4. you're having  trouble installing some software
   

CCleaner is a freeware that lets you removing your history & Temporary files very easily.

Download it from HERE. (size only 900 kilobytes)

Install it

Run it

Click on the 'Run CCleaner' button , refer following screenshot for easy understanding.

This will take some time & then all your browser and computer history, will be removed.

Hence it not only protects your privacy but also, prevents the hackers etc from accessing your passwords and usernames which might have been stored in those history / Temporary files as cookies.