I can't speak for others, but I will go through what I do as it may help to get a better understanding.
While braking, I try to keep the weight back a bit as you said, to keep the rear tyre on the ground.
As I ease off the brakes, I bring my weight forward by lowering my chest onto the tank.
This is to maximise front end grip as I approach the apex. It also helps keep the weight transfer of the bike smooth and to a minimum.
As I get on the throttle and start to roll on, I arch my back, so instead of my chest being over the front of the tank, it's over the back of the tank, if that makes sense.
What this does is put more weight on the rear tyre so I can roll the throttle on earlier, and harder.
So now I'm maximising rear grip.
I find it also helps me feel the edge of traction better.
It also gives the option of easliy shifting your weight forward again if the front is getting too light, without using the bars to pull yourself foward.
It's subtle movements, and mainly the top half of the body, but it makes a positive difference.
It also helps to be fit and have strong stomach muscles.