"For explanation purposes, let's assume the percentage of this is 20%. You are hit by an Upsmash whose knockback value at your current percentage is 100. For simplicity's sake, the trajectory of this attack is 90 degrees, straight upward. You are holding down, which grants you a vector downwards of 20 (units per frame, I'm just going to use numbers from now on)."
So, basically, vectoring is you altering the amount of knockback you receive based on the percentage of damage you were at, and the power of the move used against you. The knockback of the power of a move is, of course, determined by your weight, the damage percentage you have, and how stale that move is beforehand.
This new replacement of directional influence will definitely benefit vertical heavy hitters more, and more so for moves that hit VERY hard vertically (say Ganon's Aerial Wizkick KOing Robin at 90% off the ground). Vectoring is less helpful when you are at lower percentages, and more helpful when you are at higher percentages. Characters find it tougher and tougher to kill as percentages go up.
I'm sure you've seen many replays of the game, and you've noticed that sometimes the players have a very hard time KOing each other despite the very high percentages. This is, as stated above, because of vectoring & coupled with the stale factor of a move.
If a decent vertical knockback move should KO your opponent at 130%, your opponent can vector his or her way to saving him or herself much more efficiently than he or she can from a vertical knockback move that should KO you at 90%.
KOs will be much more early out of just the sheer knockback power of some heavy hitting moves and we'll see vectoring of many KOing moves, that don't hit as hard, at very high percentages.
All of this is if vectored downwards, not upwards.
