Yes, you need to maintain cadence, because of reasons, like saving your knees from wearing off. But if you want to win Tour de France, then you need to learn how to maintain constant speed also. Not just visually constant, not just as your computer shows, but even more constant. Speed deviates, it depends on a phase of your pedaling, but it means excessive watts lost due to visually undetectable accelerations.
Constant cadence and constant speed are different goals, the first one is about biology (how to get your body to do more), the second one is pure physics. Maybe it is even "anti-biological" thing, because human's legs are designed to push, not to pull and not to create force perpendicular to a leg. I even heard something about using gears that are not exactly circular, to help an athlete to maintain constant tension of a chain.
Amateurs (me for example) do not train for constant speed, though to some extent it comes naturally with practice. But world class athletes measure energy conversion inefficiencies in tenths of a watt, so they get a special training for this.
Constant cadence and constant speed are different goals, the first one is about biology (how to get your body to do more), the second one is pure physics. Maybe it is even "anti-biological" thing, because human's legs are designed to push, not to pull and not to create force perpendicular to a leg. I even heard something about using gears that are not exactly circular, to help an athlete to maintain constant tension of a chain.
Amateurs (me for example) do not train for constant speed, though to some extent it comes naturally with practice. But world class athletes measure energy conversion inefficiencies in tenths of a watt, so they get a special training for this.