There may be specific chord changes where the "in-line" version might work out better... none come to mind, but I am sure I have stumbled across the situation at some point.
But starting with the "Justin A" - for lack of a better term (maybe 213?):
A to A7 lift 1st finger to expose open 3rd string G note.
A to Asus4 plant 4th finger on 2nd string D note
A to Asus2 lift 3rd finger to expose the open 2nd string B note
I would note that while Justin encourages beginners to start out using that particular grip for the A to speed them along their way, as you progress to intermediate and beyond you will often end up learning and using multiple grips for the same chord in the same position. The G chord comes to mind and the "king of grip variation".
But having said that I think the "Justin A" is a viable grip to use as your standard.
1) As mentioned on page 2 of this thread, the video for Asus4 and the on-screen diagram don't match, but we should go by the diagram, not the video I will assume. Justin could be lifting finger #2 discreetly, it is hard to confirm by the video alone.
So assuming one uses the 3-1-2 A-chord fingering, the "proper" fingering for Asus4 would be retain fingers 2-1 in the second fret, and 4 in the 3rd fret.
2) Justin also mispoke at 1:28 where he says for Asus2 to "lift your second finger" but he is actually lifting #3 in the video.
EDIT on first point: I guess it doesn't matter about retaining #2 finger on the B string in the second fret to make the Asus4 since it is only the finger closest to the guitar body ("highest" fret) that makes the note, so #2 can be left on the fret board or not. This does make it easier to remember just lift up/down #4 to move from the Asus4 to the A.