Re defragmenting: yes and no. I read over in the MacFixIt Forums that while the fragmented files on the source disk are laid down contiguously on the target disk, there is something additional (I forget what) which is not done, but
is done by a defrag utility, like TTP. The difference is allegedly non-trivial.
Re synchronizing your two computers: if what you mean is that you want your desktop and laptop disks to be clones of each other,
and if both Macs can run the same version OS (if it's a generic OS installation they will, but if machine-specific they may not), it seems to me you could first boot one of them in Target Disk Mode, connect them with a FW cable, and use SD with a script to copy newer files plus ones that don't exist on the target machine. Then you'd do the same thing the other way around. I wouldn't be surprised if Dave doesn't have such a script up his sleeve already.