Animation on twos

Last day i had a talk with an animator student.
She was explaining to me the “animating on two” term, which i never heard, and i said that to me it’s the same of halving the framerate. She than said to me that it’s not the same thing because the movement is smoother than with a lower framerate.
I just don’t get it…
The only difference i can see is that if you animate on two you can always choose to add frames in some part of the animation, while if you halve the frame rate that’s it… that framerate is your limit…
Is my reasoning wrong?

p.s. Not sure if i’m in the right section, 'cause it’s not quite about animation in blender. If not move this post!

The framerate stays the same. The images are held for 2 frames each so only 12 are needed.

… if you animate on two you can always choose to add frames in some part of the animation.

Correct, but images are added not frames. One image per frame instead of one image per two frames.

You go to ones to smooth out fast action and to remedy strobing between a moving object and a moving background when both are animated on the twos. Twice as many images per second (one per frame instead of one per two frames) = twice as much work if drawn by hand or posed and shot for stop-motion animation.

-LP

Ok, I think i’v got it.
Now that i have the correct language tools i can say:
If i draw a 2 seconds animation entirely on twos at 24fps the final effect is equal to the same sequence of drawings animated on one at 12fps.
Is this sentence correct?
Maybe i can seem redundant but i really need this to make things unmistakable.

Yep. I guess it’s just that 12fps is not a standard playback speed traditionally (i.e. film/video) So on 2s worked @ 24 - as well as giving the option for dropping to ones for fast action etc. as mentioned above, if needed.