Good advice. I defrag mine once a week with Ultimate Defrag from Disktrix - Two Amazing Defragmentation Software Titles - UltimateDefrag And DefragExpress
It's by far the best defrag tool I've ever found. I run it as (Fragmented Files Only) and then (Auto), and it completely defrags the files, and then arranges them on the edge of the disk for best performance. I saw a large increase in performance by using this method.
To give you an example of how this program is superior to the windows defrag tool. Windows Defrag told me that my C: was 2% fragmented. DiskTrix Ultimate Defrag told me it was 28% fragmented.
I think this has something to do with the fact that Ultimate Defrag wants to put all of the files on the edge of the disk (which is a good thing) but I don't really know.
The reason you want files on the edge of the disk is simple. Imagine a bike tire. Wrap a string around the center of the tire and it's going to be maybe 1 or 2 inches long. Wrap a string around the edge and it's going to be 2 or 3 feet long at least. This means more data is on the edge, and the center spins at the same speed as the edge of the disk. Which means more data passes the needle per second, which gives you faster access times.