Even if you have a hard disk with hundreds of GBs, you will run out of space soon. At that time you want to see what is taking most of the space. Using Windows Explorer and going to each folder is a time consuming job. Several years back I got introduced to a tool called "Tree Size" that displays chart like bars against each folder so that you can easily see the usage. Today I found a free tool to do the same thing better – WinDirStat. Apart from bars, it displays a beautiful squarisish picture of the usage based on file types. Check it out.