Fat tires are definitely beneficial for heavier riders and heavier bikes, which electric bikes are.
A lot of people have opinions about rolling resistance, and wind resistance. I would like to see studies done.
I think fat tires have less rolling resistance on rough roads, as the tires absorb the bumps better.
If you look at the wind resistance of a rider, fat tires only increase this slightly, and it is only significant at high speed, or riding into a head wind.
Seriously, you don't think the tires on the bike in Post #54 have more wind resistance than your standard 28mm - 32mm commuter tire? Well, I do. You should too. Not just wind resistance either. Until they started putting motors on those FAT bikes they were getting most of them back because people couldn't get to the ends of their own driveways under their own power. There are just as many people who enjoy punishing themselves with the resistance of huge rubber to make them feel like they are "working for it" as there are who want to keep the same road speed as on 'normal tires' with the cush and badass looks of the big rubber. But, tbh, I don't see nearly as many FAT bikes, e-assisted or not, as I used to do a year or two ago. 50mm tires will get most 'all-road' assignments done without requiring all your energy (or your battery's) just to get moving from a stop. The law of diminishing returns is right around 2.4". Get much bigger and all the benefits of a larger section start to go away. 2.8" to 3" is very hard to justify. At 4", the size of the average FAT tire you have deffo crossed into no mans land. You are giving it all to the man and he isn't giving much back, unless you are in very deep snow or sand. Ski's for the first scenario, a Camel for the second.