Lower BBs are in fact more "aero".

Lowering your center of gravity relative to your wheel centerline also improves stability on paper. I'm not sure that a few mm make a big difference but having raced on a LeMond and a custom steel bike with a BB drop difference of 5mm, the lower BB seems to make the bike feel more planted.

I believe the UCI has rules govening the BB drop on bikes (or course) but I am not certain of the dimension. Track pursuit bikes usually have a BB drop of 7cm, mass start bikes are about 6-6.5 and Sprint bikes are 5-5.5.

-SD

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https://www.kickstarter.com/...bike-for-the-new-era

My personal preference is for 8.0cm drop on the road. Like it much better on descents.

My new bike also has an 80 mm drop and is very stable. That saying something on a frame with an 81 degree seat angle.

I think the biggest benefit is stability. While you may get some aerodynamic benefit by lowering yourself down behind the front wheel, it makes it tougher to get the torso low. With aero tubes it is hard to get a head tube shorter than 10 cm, and for every centimeter you lower the bottom bracket you are effectively reducing the handlebar-seat drop 1 centimeter. I wonder if this is why Cervelo's BB drops are only around 6 cm...