Over simplifying a bit---Deflexing off the handle adds smoothness to the feel of the bow and reduces fingerpinch at full draw while making the bow easier to string. Reflex increases preload,which allows more energy storage thus adding arrow speed but can reduce "stability" making the bow harder to shoot as consistently. The Deflex/Reflex profile is merely a compromise trying to pick up advantages while cancelling some of the disadvantages.... And it works pretty well. A Deflex/reflex will handle like a longer straight limbed bow while shooting faster than a longer straight limb (assuming it is all done "right").