Jax's dash punch is one of his very useful move because of how far this move can have you travel across the screen. On block it is technically -6 and that is very hard to punish with most characters. Even then, if you were to space out the dash punch, it would push them so far back that they probably couldn't punish it. The ex version of this move give him armor and would mostly helping you get in against projectile users.
Combo wise, dash punch is probably more of a combo ender in your midscreen combos. It will usually push them closer to the corner, but there are other moves you could replace with dash punch for the same corner carry.
The only thing about this move is that it doesn't have the greatest hitbox in the world and can be ducked without block sort of like projectiles in Mortal Kombat X. This can make dash punch punishable, but this requires a read from the opponent, so don't get too predictable with your dash punches.
Jax's dash punch is one of his very useful move because of how far this move can have you travel across the screen. On block it is technically -6 and that is very hard to punish with most characters. Even then, if you were to space out the dash punch, it would push them so far back that they probably couldn't punish it. The ex version of this move give him armor and would mostly helping you get in against projectile users.
Combo wise, dash punch is probably more of a combo ender in your midscreen combos. It will usually push them closer to the corner, but there are other moves you could replace with dash punch for the same corner carry.
The only thing about this move is that it doesn't have the greatest hitbox in the world and can be ducked without block sort of like projectiles in Mortal Kombat X. This can make dash punch punishable, but this requires a read from the opponent, so don't get too predictable with your dash punches.