If you're doing enduro, downhill, or aggressive trail riding, rubber or Vibram-soled MTB shoes are usually the right call. These shoes have a stiff internal midsole for pedaling efficiency, but the aggressive rubber lugs on the outside give you serious traction when you're hiking steep, loose, or muddy terrain off the bike. That grip can be the difference between confidently scrambling up a slick incline and slipping all over the place.
The trade-off is that rubber/Vibram soles flex more than carbon or nylon race soles, so you'll lose a bit of power transfer on hard pedaling efforts. For cross-country racing where you barely step off the bike, a stiffer sole makes more sense. But for gravity disciplines where you're constantly getting on and off the bike, checking lines, or hiking to features, the walkability and protection are worth the slight efficiency trade-off.