Automated Extractors means no drones for vespine, I like it for it helps accelerate my base building and the faster you do base building the quicker you can do army building. It also means less "silly" micro-managing.

1) In the beginning of the base building automated extractors save you 3 drones for each vespine area, so if you have two vespine areas that is six less drones which you need to worry about, allowing you to have your drones focus on minerals or creating buildings for your tech tree so you can create your army.
2) When you expand to your second base you can just grab 3 or 4 drones and have 1 drone create the hatchery, and 2 or 3 drones create the vespine collectors. Thus you get your vespine faster.

I always choose twin drone instead of vespine efficiency (25% more vespene). I really really hate base setup so getting it over as soon as possible is something nice the twin drones allow.