just a fad fashion statement?
The tight jean, scarf wearing crowd needed something to ride on the trails when their fixies are in the shop getting their handle bars cut down a little more.
Originally made to ride on snow which in turns means they work really well on sand. The Simpson desert classic also split their rankings to those on fat bikes and those on regular bikes.
The other place they kind of work well is offroad touring. You can go fully rigid but still have something resembling suspension from the giant tyres and bucketloads of traction.
I think the rest are just strange folks that want something a little different. They'll claim more 'float' from the large tyres at low pressures and stuff like that but really they're just odd.
I'll probably add one to the shed in a few years, more than likely a Muru of some sort. I'd like to do the Simpson desert classic at some point and I'd like to do a bit more bike packing. I'm not in any real hurry though.