Yup, there is plenty of documentation on this elsewhere as well.
The Best Drones
"Overall, the Phantom 3 is a much better flyer than its predecessor. The new ESC motors use what DJI calls “active braking” (when you reduce throttle, the drone actively reduces motor speed instead of just cutting power and letting the props slow down); in practice this means that at full tilt the Phantom 3 can stop on a dime, which prevented us from crashing it headfirst into a window or two."
Do a web search... ;-)
RedHotPoker
yes, but this example again proves my point instead. Think about it, a quad moving forward at 50KmH, how do you stop it on a dime ? Not by slowing down, let alone stopping the propellers, but instead by providing thrust in the opposite direction. Newtons first law. What the active braking setting in the app seems to do, you can do in attitude mode with your sticks too, instead of letting the quad coast, just give full opposite control until the forward velocity is bled off. This "braking" requires extra thrust from all 4 props.
In fairness, motor braking does improve responsiveness overall, so there could be a marginal benefit even in the described scenario, the quad may be marginally quicker to transition from forward to backward pitch angle, but stopping on a dime in GPS mode is certainly not the main attraction of motor braking. Perhaps DJI chose to market this as something its not, because it would otherwise be too confusing, but as a result, its certainly confusing to me.