1TB drives = more pr0n... i mean, storage...
Seriously though, if you store a lot of stuff, or have large files to contend with, higher density storage helps, it's cheaper, more space and power efficiently to go with larger drives. Typically anyway.
To defrag a large drive, shouldn't take days, i assume you are using the built in windows defragger, in which case, yeah, it's slow. Diskeeper defrags much faster and in only one pass. The extra monitoring it does only really works if the drive is used regularly and left hooked up for extended periods - and you need it to be ultra clean 24/7. After a while though, the amount of work required on the drive drops exponentially to a small 5 min check every now and then, depending on usage. It likes to juggle files around so that unused files are put at the end of the drive, and it's that process that can slow things down.
The good news is, you can disable the Inteliwrite etc, and only use manual defrags on external storage. And yes, it's smart enough to know that a different drive is in the dock, as soon as you unplug it, it'll notice, since it changes the model number, it just thinks it's another removable storage device. Just remember to run the safely remove process, otherwise you good yank it in the middle of a defrag.
Using a dock for <1TB.... makes no difference. Docks/enclosures just slows the defrag process down a little due to the interface. eSATA and USB3 will speed things up a bit, but not by a huge margin, at least for defragging anyway.
Those docks are cool, i have the USB3 one for when i get new MB sorted, works fine over USB2 too. I just disable the real time monitoring on diskeeper for removable drives- it leaves them alone so i can't run a manual defrag every now and then - for when it's needed anyway.
Or maybe I am a prime candidate for 