Fat tires excel on all soft surfaces, but they were originally designed specifically for snow. It works the same way as snowshoes - by spreading your weight over a larger area. I ride year-round, and the difference between my two bikes is huge: one has 2.5" wide tires, the other 5.05". The fatbike can handle snowy trails that are difficult to even walk on, and I’ll even let some air out of the tires to make them softer and increase the contact patch even more.

You're absolutely right about the extra friction from the wide tires - it’s like dragging a car tire behind you. That’s why my fatbike has electric assist. Pedaling that thing through soft snow without it would be pure torture. Unless you plan to ride in snow, sand, or mud on a regular basis, a fatbike really doesn’t make much sense.