It's all about the amount of friction you have between the tires and the road. On dry pavement in a straight line I favor the front, but when on a turn I favor the rear so that all the friction force on the front is being used to keep the steered wheel on track. The front brake provides something like 60% of your stopping power and will stop faster then using just the rear.

On wet or slick pavement same idea, I do not want the front to slip. For me once the front slips stability and controllability are greatly compromised! (As in, I slam to the ground unless I'm really on my game) However the rear does not affect steering or stability if it slides about (in a general sense, and usually any looseness can be controlled), so I use the rear especially in an emergency stop.

Things I don't need to think about for another five months!!!