Faster cadence does not mean you are going faster. You might just be running up and down on the spot. But it does improve a lot of the key elements of running form that will enable you to eventually run faster with less effort, because it takes full advantage of your bodyweight, your momentum, your elastic tissues, to get the most out of every landing step. We want to be using the 'free energy' from the ground so that we don't have to create so much ourselves, using our own muscular energy.