>>>is this true
Not really. It can free up a bit of space on your hard drive but, given the massive size of modern hard drives these days, that's probably not really an issue for most people.
The main reason that people clear their browser history is to prevent others from seeing what they've been doing. (It doesn't have to be anything 'naughty'. Someone might, for instance, not want their partner to know that they've been looking at websites advertising weekend breaks in Paris, in order not to spoil a surprise for them).
The way that browser histories are cleared varies between browsers. Instructions for all of the most popular ones can be found here:
http://www.computerhope.com/issues/ch000510.htm