Originally Posted by Wraith Rider
The rear brake is powerful enough not to need engine braking. Also the braking power is more easily controlled when the engine doesn't interfere, especially if it's nearly stalling.
I was told in riding school to pull the clutch but not shift down because it's better to focus only on the braking. I think that might be good advice for beginners, but never liked it for myself.
This. The key word in the OP is 'emergency'. The rider has all of his/her focus on making the stop and avoiding the source of predicted initial impact. Disconnecting the engine allows the proper braking feel to keep the tires doing their best. A connected stalled engine does not allow proper modulation of the rear brake. Nothing quite like getting off the brake of a sliding rear wheel only to have the engine fire with half throttle in a tall gear.
The dowside of this teaching method for noobs is that they tend to have a more severe panic reaction tensing up and not being able to modulate the brakes and steering much less think of options while in the moment.
Even exerienced riders can get so 'caught out' in an emergency stop that they execute it poorly due to lack of practice. I can't remember when I had to make a full-on 100% emergency stop? My riding habits are of a sort to keep me from ever having to execute that again. Now that I have typed that, watch me come around a curve and hit a moose due to being so stunned by the sight that I will have completely forgotten how to ride and years of making great habits totally fail me. Sigh.
BTW, many emergency stops for experienced riders do not end in a complete standstill. Some riders are looking for 'outs' and 'safety holes' while braking hard. Commiting, or having to commite, to nothing but a full-on braking is a pretty good sign that one is still a noob in the situational awareness area of riding. And that does not excuse the experienced rider from further regular braking practice.