This is just my perception, but on my fat bike in snow, it "feels like" 1 mile of an "average" ride is the equivalent physical effort of 3 miles on my hybrid or mt bike with "normal" tires during the "regular" season.
The longest ride I went on on the fat bike was about 36 miles and I was beat when I got home - felt far more physically draining than the day I did my first Century on my hybrid.
One other advantage in the winter - I indulge in a good breakfast on the ride, usually pancakes, something I do NOT allow myself the rest of the year when it's lean proteins and low carbs.