When we cycle, the power from our legs goes to our heel, but we want that power transferred to the ball of our feet where the pedal is.
Having a stiff sole between the heel and the ball of our feet means that less of that power is lost, increasing our performance and comfort.
Many cycling shoes are designed to clip into a special kind of pedal, meaning that when clipped in, we can lift the pedal up as well as push it down for a more efficient pedalling movement.
Just as there are different kinds of bike, so too is there different kinds of shoe. Some shoes, like road cycling shoes, might be designed for on the bike only, specifically designed for an increase in performance and efficiency. But others, like mountain bike shoes, may sacrifice that, in order to be able to walk more easily and step over obstacles.