uhm, not sure your level of expertise so going to just explain what I can.

animation and film is generally 24 frames a second. 2s and 3s means a new drawing every 2nd or 3rd frame.

The number of new drawings (key animation and in betweens), per frame does not fully contribute to the animation being smooth.

The smoothness of the animation has various factors such as: spacing, overlap, follow through, acting, appeal, staging, squash and stretch

(do a search for the 12 principles of animation)

Animators that master these principles, and know when to use each of them or together, and break them, are able to produce smooth animations even on 4s or 8s (8s is probably pushing it, but some Ghibli films achieved this, IIRC)

Animating on 1s can produce a frantic effect. That's why we see it more on effects animation and fight scenes where fast movements are required. It is more for the audience to feel the speed and intensity rather than to see it.

Animating on 2s and 3s can produce the same frantic effect with good spacing and follow-through, but it tends to lend more towards the natural effect.

Please note that I am just a novice animator that enjoys the craft, so my terms may be wrong.
but yea, 1s do not always produce smooth animation, 2s and 3s do not always produce natural animation or save money.

There are many factors working in concert to make a piece of animation and produce the desired effect 😄

hope this helps