This makes me so happy that I learned to L-cancel with Z.
If only I had a CRT I could use my apparently better L-canceling method to play the game.
Juggs is right as far as I can tell, and I'm not just saying that as Juggleguy's friend. The first frame after jump squat is over is an interesting one as far as what it means for actions and states-
If you are holding X/Y/Up on this frame, you will Fullhop instead of Shorthop
Jump velocity is applied on this frame, and takes effect on the one after
Your character is very technically airborne, and all air actions can be input and they will begin to carry out on this frame
No ground actions that are normally possible during jump squat are so on this frame
Your character is concidered in an air state for moves that have different hit data on air or ground hit, such as DK's ground slap, that does not hit air opponents, and when hit by moves below a certain knockback threshold, such as shine, you will land on the ground instantaneously with no hitstun after hitlag is carried out.
Jump "sounds" come out on the next frame
Your character's TopN bone is flush with the ground on this frame
This is what would go on to become the "Dead frame" issue in Brawl
So, you are barely technically airborne, but your character does not get any sort of vertical movement on this frame. You do not have to be rising to wavedash, and perfect wavedashes should be near silent (That goes double for you Ice Climbers).
If anyone else knows more about this frame and frames surrounding jumps please feel free to add-on, or correct me where I am wrong.