FYI read this from CCC
A welcome side-effect of cloning one volume to another is that the files on the resulting volume are largely defragmented. While fragmentation is not as significant of an issue as it used to be (e.g. in the Mac OS 9 days), people that have begun to fill the last 10-15% of their boot volume may see some performance benefit from defragmentation. If you find yourself in this situation, this is also a really good time to consider migrating to a larger hard drive altogether.
Defragmentation is a natural result of backing up your data to an empty backup volume. Simply prepare your backup volume for use with Carbon Copy Cloner, then use CCC to clone your source volume to your destination volume. Note that a block-level clone would actually preserve fragmentation, so don't choose a block copy if you're looking to defragment your source volume.