Comment on iDefrag

From Developer:

iDefrag respects the "Hot File" zone so it will not slow down OS X.

OS X's automatic defragmentation is good, but has limitations; it won't defragment free space, files larger than 20 MB or files with fewer than 8 fragments.

Also, iDefrag will optmize your hard drive, moving OS files close together, which can make a difference.

Of course, your mileage will vary. See our web-site for more information.