Hi Steve,
Pull the trigger full to get full speed.
You reach a corner and have to reduce speed.
Now if you release the trigger fully it will brake to reduce speed like any regular controller.
When you enter the corner you have to pull the trigger again for let say 50%.
So you go from 100 to 0 to 50% to enter the corner.
This means lot of trigger travel and time.
Now with regenerative breaking.
You reach a corner and release the trigger to 50%.
As the regenrative brake hysteresys is set to 5% it will activate the break from 95 to 50% and then release the brake and go furhter with the speed of 50%.
So with this option you can brake later as you only release the trigger to the point you need to round the corner.
This reduces trigger movement time and also make the driving and control more smooth.
The hysteresys can be altered.
Now we also have speed brake.
If the trigger was pulled fully you carry more speed so you need more brake to reduce speed.
If the trigger was pulled 50% you carry less speed so you need less brake.
So speed brake is a speed dependable brake value.
Do you understand? 
Paco