Someone once made a good analogy between weight training for competitive powerlifting and training with a power meter for performance cycling which went something like this: imagine trying to optimize a powerlifting training program where you couldn't see the numbers on any of the weights or even tell how many plates were on the bar at any given time.
Sure you can lift more and more until it feels 'heavy' or you just can't do any more, but most folks can probably imagine there's benefit of quantifying your workload and tracking progress from one workout/week/month/year to the next.
Most folks can probably imagine there's benefit to using independent cranks, too. So... there you go.