Can be useful on certain tracks where speed on the straights and traction in cornering is needed. This refers to a tire that is wider than most tires, say 2.25 and over. Usually a knobby design, sometimes a hybrid, these tires are for downhill, mud, loose surfaces, and wet conditions and overall use. Any wide tire has to have room to fit on your bike. It must not rub the chainstays, front derailleur, or brake housing.
Some riders like to ride fatter tires in the front than the rear.
I prefer fatter in the rear than the front. They weigh more than narrower tires, and have more rolling resistance. These tires may offer good traction when climbing, but because of their weight it may be harder to pedal uphill. It may be noticeably harder when staring the bike from a stop as these tires require more effort to get rolling. Their extra weight can give your more momentum when going downhill, and offer more floatation over boulders, bumps, and rough surfaces.