Radial slicing gets the same results with less effort.

There does seem to be a pretty good difference in how diced it looks when you do it, though? Demonstrated here

I went to culinary school, they do teach the horizontal cut method, and it is indeed inferior. Plus it lowers your yield, is more dangerous, and produces an inferior end result. All one needs to do is look at how the layers of an onion are constructed to see that it’s stupid.

My preferred is the angled lengthwise cuts (starting at roughly 30 degrees, straight up and down in the middle, and ending at roughly negative 30 degrees). The angle isn’t super critical. Then, so your cross cuts. No faffing about with the pieces hanging from your initial lengthwise cuts and then trying to do the horizontal, and produces a better “dice” (you rarely get perfect cubes with any method anyway).