I do a LOT of DVD ripping, transcoding (using handbrake), and moving of files on to NAS on this machine.
A few people will say that since you're deleting or moving all the files the fragmentation will be minimal, except I do them in batches on an as and when basis. The disk frequently gets to 90% full, then I do some encoding and ripping.
Needless to say, I expect it to be fragmented. I run KDE on it, it's a DHCP/DNS server; I read emails on it, run Chrome and other apps. If this was windows it'd be SLOW.
So I run fsck.ext4 -nfv /dev/sda1 and what do I find.
654 non-contiguous files (0.3%)
331 non-contiguous directories (0.1%)
In my opinion, that's pretty damn good. I'm impressed again. Linux and EXT4 rule bit time. No wonder there is no mainstream de-fragmentation tool for EXT4.