The more flexible you are and the greater core strength you have, the more saddle to bar drop you can comfortably ride, and the more aerodynamic you will be. There are other benefits as well such as recruiting stronger muscle groups. Don't get sucked into the 'slam that stem' mentality though that's rampant among cyclists. Ride what's comfortable. An aggressive looking bike is worthless if you don't ride it because it's uncomfortable. I found that the more I ride, the lower my bars can be in relation to my saddle.