Your three-word question is by itself ambiguous. If your question is a reaction to the fact that the description of this device uses both words Desktop and External in its name - my understanding of this is that this is an external drive (enclosing the drive in a plastic and metal package) that relies on AC power (using a AC->DC power supply) and thus is suitable for a desktop system. The drive within the enclosure can be removed and mounted as an internal drive in a desktop system - all fifteen of the drives I've opened have a ST4000DM000 drive inside. This drive includes a USB3.0-to-SATA3 adapter that is easily removable, exposing the SATA3 data and power interface.
with the speed of usb3 and thunderbolt, external is fast enough for me. While my mac pro has 4 drive bays(maxed out)and it so much cleaner than having these external drives all over the place, technically speaking Im very pleased with external drives. This seagate is a great product.
My answer is that it's a toolbox. I only went for external because both of the drive bays on my desktop are already being used, one being a 120gb drive and the other a 500gb drive with both being close to full. The other factor was price, which for the drive plus the external enclosure is actually cheaper in some instances than a bare drive of similar capacity by itself. Otherwise, the fact that it's USB 3.0, I'm not seeing a problem with the speed of my data transfer. I'd say if you don't already have the space for a spare drive in your desktop and if the price point isn't also already reasonable for a bare drive, then go with the external option (and I guess at least this model).