What do fat tyres actually change?
Wide tyres can provide a distinctive combination of cushioning, grip and stability. They can be appealing on loose or uneven surfaces and for riders who value a planted feel.
They are not automatically better
Wider tyres can add rolling resistance and weight. For a smooth, fast urban commute, a lighter setup may be more appropriate.
Where they make sense
Mixed surfaces, gravel-style paths, leisure riding and rougher routes can make the extra volume useful. Tyre pressure also changes the character of the ride.
Choose the bike around the terrain
The most useful comparison is not simply tyre width. Consider motor assistance, battery, brakes, geometry and the surfaces you actually ride.