I wasn't really pushing for this during Draenor as I saw collecting the parts impossible. You need to collect 3-4 parts per module and you need to get 4 modules... um yeah, nevermind that rubbish!
Yeah I know you can just buy the parts if someone is selling it but I never did while Draenor was current cuz those pieces were hella expensive on the AH at the time. I was slowly collecting the parts when I was going back and doing Draenor stuff. The parts drop from mobs.
If you didn't know what this does, it brings and Auction House NPC to your garrison. There really is no reason to complete this now. BUT just completing useless things ingame brings me great satisfaction. I think I would find having this very useful if you like to work the auction house or you make most of your gold from selling gathering mats. My AH Dreanor mats are not the best prices tho. But oh wells, I can now say I have an AH in my garrison. I have not steadily worked the AH for a really long time. I would literally spend hours sifting through items, buying them and then turning them... anything I felt was underpriced. Thats how I made most of my gold... and of course farming on my own. :-)
But anyways, YAY for my garrison AH!!! I am so happy.