I followed this guy's instructions of defragging and just to be clear defagging is rebuilding your directory right? Cuz Discwarrior does not have a defrag option...
In short, your drive's directory is its address list for everything written to that drive.
Imagine if you had a room full of file cabinets chock full of folders with pieces of paper in them, and on the door of that room is a directory that tells you exactly which piece of paper, in which folder, and in which cabinet the information you need is written on.
Now imagine that you spill coffee on part of the directory and it becomes unreadable. You've just lost information because you can't find it anymore. The info is still in a folder in the room somewhere, but you have no idea where to look. You now have a corrupted directory.
Disk Warrior may be able to solve this problem. It keeps the directory neat and efficient if you just use it for maintenance, and it can often recover files lost due to directory corruption. It can also rebuild partition tables.
Now, imagine that you have a book saved in the filing room, but it's big, so when it was filed it was split into pieces. A few chapters are in one folder, a few chapters are in the next cabinet over, and the rest is in a cabinet all the way across the room. When the hard drive does this to a file, that file is said to be fragmented. If you have a bunch of fragmented files scattered all over your drive, you use a de-frag tool to move everything around so that, in this case, all the parts of the book are stored next to each other, in order.
A hard drive that is excessively fragmented will take a lot longer loading the information you need to, in this case, display in-game graphics as a toon moves from one area to a new one. That's because it needs to find each piece of the file, no matter how far apart they are scattered, and then assemble them in order. In short, fragmentation equals a slow hard drive, which equals degraded computer performance.
I use Drive Genius to do de-fragging on my Macs. Critical Note: ALWAYS BACK UP YOUR DRIVE before you de-frag.
Defraggers copy things, move them to other places, and write over stuff. When they screw up, if you didn't back up, you are screwed.
Drive Genius does a lot of other stuff, as well. It's a well rounded, if a little bit flashy, drive utility. In my opinion, however, Disk Warrior is far superior for recovering from any kind of directory snafu. Disk Warrior has fixed problems for me that neither Apple's Disk Utility nor Drive Genius could touch. Disk Warrior once fixed a drive for me that couldn't even mount to the system. Neither Apple's Disk Utility nor Drive Genius could even see it, and Disk Warrior fixed it.
FYI: I have no association with the companies that make either of these products. There are other utilities available, these just happen to be the two that I've used ever since I experienced my first drive related issue on a Mac, oh so many years ago...