Short cranks for aerodynamics (especially for better positioning) is the primary reason that bigger riders use short cranks. Shorter riders, on the other hand, can often produce greater torque by switching to shorter cranks. If you're a finesse rider and can spin like crazy (a spinner), go ahead and use long cranks. If you generate power with high torque and force, or want to generate higher torque and force, short cranks. It's pretty obvious.
Last edited by tobukog; 07-22-17 at 07:23 PM.