Clearing the cache is usually the first step in fixing certain issues that may arise during your browsing experience. Things seem to slow, websites may not load properly; although rare this does happen and keeping your browser's cache clean on a regular basis (especially after heavy internet usage) can alleviate a lot of issues.
First, what does this mean?
Your browser's cache is pretty much a collection of data collected during your visits to various web pages, this includes location, browsing history, pictures and other media that browsers tend to load in the back ground, and other store information for later use (this way the website will know you have visited it's page from this computer before).
Here is a short tutorial on how to remove and clear all of that excess data: