For most social Tango, step-by-step, or basic-by-basic, figure-by-figure lead/follow can make plenty of sense. Nothing is wrong with it.
But then, there are songs that are fast (like many Vals), or with a lot of energy (some milonga and Tango), or Tango songs with changing energy flow. You'd want to translate the musical energy and its flow to your dance.
Then, what do you do? One way to do it is to use energy/momentum lead/follow.
A critical ingredient is a good follow, who already has all basic body usage, basic steps, and (at least some) figures by muscle memory. And as premises, (a) she can use them with music or by lead, and (b) she can switch the speed and size of her moves, according to music, lead, or choreography.
Another critical ingredient is a good lead, who also has all basic body usage, basic steps, and (at least some) figures by muscle memory. He also should be able to use them with music, to lead them, and can switch the speed and size of his moves and leads.
Now, instead of using a step-by-step tango, he can just draw his and her traveling paths as lines on the floor in three-dimensional manner. As both do not have to worry about stumbling, he can just cue the next move, and she can just dance it.
A starter example would be, a basic salida. "Side-walk-walk-her cross/uncross-exit" can be done in one continuous flowing motion for both (perhaps with a little pause on the cross for proper phrasing).
Another example is her molinete/continuous giro with his lapis or enrosque. She will be doing her grapevine steps (side-back-side-forward), walking around him. How big her steps are, how deep she pivots, and how fast she moves, depend on the music, the lead, and resulting momentum. Yet, this can be done in one continuous motion with flowing energy.
Your muscle memory and quick yet responsive feet will allow you to create and ride the momentum/energy on the floor.
Tango basic moves are based on either (a) walking or (b) pivot on axis/rotation. You use body weight and counterbalance to move and draw energy line, and to create dynamic moves and further momentum/energy as a couple. Hardly any tiring heavy muscle work (like lifting weights in gym) is involved.
When we watch an "improvised" demo dance by professional Tango dancers, they are usually using energy/momentum lead/follow one way or another.
After all, they are on the floor with plenty of spaces around. No need to worry about outrunning and colliding others. And they are supposed to demonstrate something impressive. Then, they use energy lead/follow, which looks much more dynamic, dramatic, and perhaps sporty, than social dances on crowded floor. And spurt of energy can look like a proper musical interpretation if used right.
In fact, they have stockpile of moves they memorized by muscle and can use at will, both in slow and with energy/momentum lead/follow. That is their trick to it. (No tricks, really).
So, do you want to use the energy/momentum lead/follow? Sure, it is still well within a social tango technique and vocabulary (or execution of them). And your dance can look more "advanced".
I say again that there is nothing wrong with a step-by-step, interactive and slow, even intimate tango. A lot of times, such tango is favorable on the social floor to a sporty, showy, but maybe less intimate, dance.
Actually, if she does not have good muscle memory to pull off flowing moves but you try energy/momentum lead, the dance can fall apart.
I'd say, vals is a gateway dance to energy/momentum lead/follow. Fast vals can be a test. Gotta be careful.
But when the song, your partner, and/or choreography call for it and permit it, just use energy/momentum lead/follow. You do not always have to drive under 40mph. Step on the gas pedal and ride the momentum. It is an extended option in your technical arsenal and provides a different kind of tango fun.
PS
Lead has to be absolutely sure about what he is doing. It helps if you can verbalize for each set of momentum lead flow. Like "Lead molinete", "lead salida", "lead giro then sacada to switch position", "lead to mirror position then gancho", etc.
