Streets and roads aren't useful only for wheels. Try taking a mile-long walk through a (seemingly) flat field and through a paved surface as an experiment.
The first one will be much bumpier and tiresome than the second for any given speed, and you'll be at a higher risk of injury due to careless step. And the benefit of having a flat surface is greater the more rugged is the terrain that must be crossed. This is why, though the Incas didn't use the wheel, they had roads nonetheless. And the Romans, too, built their own roads mainly for the speedier movement of their armies while on the march.
The first one will be much bumpier and tiresome than the second for any given speed, and you'll be at a higher risk of injury due to careless step. And the benefit of having a flat surface is greater the more rugged is the terrain that must be crossed. This is why, though the Incas didn't use the wheel, they had roads nonetheless. And the Romans, too, built their own roads mainly for the speedier movement of their armies while on the march.