On my daily life, I deal with VM Images and File processing.. Large files.. This causes my MacBook to slow down due to Fragmentation… My solution was always to backup to an external drive and restore back, and it solves the fragmentation problem and the MacBook Performs better. However, this takes really long time. Especially with large disks. Today, I tried iDefrag from Coriolis Systems. I purchased the Application using Paypal and gave it a try. It worked like a charm. It took 4 hours to finish, but I can notice the speed of my VMs. And Apps load a bit faster. Good Application to keep the performance of your Mac OSX.
Keeping in mind that your Mac OSX defragments any file less than 20MB automagically, however, large files get fragmented, to defragment, you can move the files to external disk and move them back. However, this takes time and requires you to have an external disk to backup the files.