Necessary? No.
A very nice luxury while towing or hauling heavy in the mountains? YES
Put a BD brake on my Ram last year before the trip to AK. After 1700+mi of hauling the AF with a 7klb trailer in tow, the front wheels on the truck barely had any brake dust on them. By comparison the wheels would have been brake pad colored without the EB.
At $1200 it was not cheap but it sure is nice to pull the switch headin down a long grade and just fit back and coast to the bottom. No downshifting and no service brakes needed at all to maintain speed until the grade gets about 8%. It'll hold back 18k gross Rollin on 6-7% grades all day.