I learned it early on. Naturally we all want to stand up and not stoop over, it's uncomfortable sometimes but necessary. I used to lightly brush my chin and occasionally I'd whack myself on a power stroke.
I dunno if there's scientific evidence it's better, but it's common sense.
It's easier to see how thickly you're cutting the object ball, and where you're placing the cue tip, when you're nice and low on the shot. On a longer shot, you can get the tip, the cue ball, the object ball all, and the pocket all in one 'shot picture'. But if you stand upright you may find the OB/pocket are way at the top of the picture, while the tip and cue ball are way at the bottom. You can't keep them all in view at the same time when standing upright.
In old westerns you might see guys firing from the hip, but watch competitive archery or pistol shooting, they get their eyes where the barrel/arrow is.
PS: 1ab has a point about old-time players standing upright, but there's usually a reason if modern players do something differently than the old-timers... in ALL sports. In this case it's probably because in the old days people played straight pool, and if played well the game rarely has a lot of long 'testers' whereas you might shoot a long shot every single game of a race to ten in 10-ball.
Good on you for letting go of your ego and being receptive to instruction and checking things out for yourself. IMO this is part of your fundamentals and you cannot choose to put it on the back burner.
I find this stroke to be very stable.
