While a fatbike is a lot slower on smooth paved roads, they can still be a lot of fun. My commute is 18-21 miles 1/2 gravel the other half paved. When the gravel is in bad shape, the fatbike is my preferred ride. When the gravel is packed and smooth, the fatbike is not the fastest, but I will sometimes take it anyway.

I've also done some touring on a fatbike. While not the best choice for paved roads, it does open up alternative routes. So short answer, ride what you want and enjoy.