Aerodynamically, you are at a disadvantage with inverted roller coasters. The coaster trains essentially resemble a large rectangle, and have lots of air drag.
The excitement factor however is enough to make you throw all physical concerns to the wind - the inverted coaster was the first truly bold step outside of the normal sitdown train (Stand-ups were still in their infancy), and opened an entire new world of possibilities for riding positions. While the predecessors such as the bobsled, suspended swinging, and initial stand-up coasters had been tried to reasonable success, all of them were no match for the madness that ensued with inverted coaster design. B&M for instance was able to keep the ball rolling and begin investing in true Stand-Ups, Floorless, Flying, 4D, and Winged.