I'm no expert, but I've come to believe the braking is almost entirely
regenerative under normal conditions. Some people have the Coastal
Electronics friction brake indicator light and they can tell you more about
it than I can. We know it reverts to friction brakes at low speed, when the
stopping called for is harder than the regen can do, when the battery is
"full" and when going over bumpy surfaces. Otherwise, I don't think the pads
get much use.
Using the B setting will definitely burn off energy, but it will do that
whether it needs to be burned off or not.