Disclaimer: I don't own fat tire eBike nor have I ridden a fat tire eBike
Qualifier: I own two fat tire bikes and ride them
The following is only a personal opinion and to a degree an attempt to have fun.
It is logical but one must say that compared to regular bikes, Fat bikes are slow. The tires are noisy on the paved road. Pedaling a fat bike on a paved road, to a degree, makes you feel like that guy:
having said that
Fat bikes are great fun on the beach where regular bikes can't go and where mountain bikes experience hardship. Riding one in the morning at low tide with the joggers and walkers while the sun is rising (east coast) is pure bliss. Find a long enough beach (our longest is 7.5 miles) and you got yourself a nice 15 mile bike ride.
Fat bikes are great fun to ride on snowmobile trails and snowshoe trails. Find a trail with mild, rolling hills, through a forest that acts as a windbreaker and you got yourself a nice way to spend a winter day.
Fat bikes are great fun to ride on mountain bike trails. They roll over roots and rocks better or comparable than a mountain bike (sort of). For me, ideally on moderate ups and downs.
Fat bikes are great fun to ride downhill at ski areas where you can take them up on a lift - disclaimer - I have never done that
but I have biked and hiked up a mountain and rode the bike down. I wouldn't want to say that hiking a fat bike up a mountain is great fun though haha.
Fat bikes are great as an access vehicle to remote locations that lack nice hiking trails but have dirt roads. Awesome on this type of multiday camping bikepacking trip.
Here is where I think fat tire eBikes would be really great:
Snow and slightly deeper snow.
Fat biking in new unconsolidated snow is pretty much bad. No matter how wide your tires are or how fit you claim to be you still breathe a sigh of relief when you get on more consolidated snow. the deeper the snow and depending on your fitness you will not be able to ride some of it. Adding electric motor to the mix will give you the extra percentage to ride in deeper snow and of course on snowy uphill section you would have had to hike up.
ebike Fat biking in the snow could be great if your commute is on unpaved roads. That means that after a few winter storms you either have to hike the trail with snow shoes to pack it down or stop riding altogether. Adding eBike Fat Bike to your commuting mix could extend your biking season and add another fun twist to the route.