The dolphin kick is one of the hardest things to learn, but also one of the most fun things to do in the pool.
In fact every time I get into a new pool, or even the ones I'm used to, the number one thing I do first is often dolphin kick. As an instructor it is tricky to teach it because it is a full body movement, but you're also not swimming either. Sometimes called mermaid kick, or simply the kick for butterfly stroke, but the dolphin has two forms. That being the red wave, and the blue wave.
Why + Philosophy:
Noticing over the years that some students were more speedy, and others more built for endurance. It lead me down the rabbit hole of sprinters vs marathoners in genetics.
That being the dichotomy of going fast for short distance, or slow for long distance.
How + Physics:
When it comes to the dolphin kick you either do swift-tight, and fast twitch dolphin kicks = blue wave, or you do elongated-slow, and slow twitch red wave.
These blue/red waves originate from the concept of light physics on the visible light spectrum. Red being the slowest, and blue being the fastest.
These are how I differentiate the different kinds of dolphin kick based on your physical genetics. For example I am a sprinter naturally, and so I gravitate towards blue wavelength style dolphin kick. I like going fast.
What + Psychology:
One thing to keep in mind is that you aren't supposed to isolate yourself into one of them. Rather using this as a stepping off point for gaining the opposite of what you're naturally good at.
Meaning dolphin is a good example of sprinter vs marathoner, but it isn't the only one. Especially in the case of swimming, but even in other areas.
Take into account the dynamic of what you do best, and then go outside your comfort zone and do the other.
Mastery over dolphin will lead to more fun, freedom of movement under water, a faster glide transition, and more. Gaining a fundamental understanding of red wave vs blue wave, and teaching yourself to do both; That will lead you to a greater mastery over swimming as a whole.
This slow vs fast debate isn't one over the other, for it is both that are necessary.
This is advice for people to level up their swimming, or perhaps get started in the first place. While you swim you should make sure you are doing so in a public facility with a lifeguard on duty for safety.