A primary reason for this is that ALDI products (at least here in the US, I don't remember whether this was true shopping in Europe a few years ago) typically have 4-6 barcodes per package--a box will often have a bar code on every face, if it's a house brand product. Makes for extremely fast scanning, true.
I also just noticed the dual-conveyor model in operation at a newly-opened Lidl near me yesterday. ALDI here typically doesn't do that--most stores are set up to place groceries (and unfilled bags) directly into a customer cart, and have a nearby counter to bag your groceries at.
Their scanners also don't suck. IBM used to make very high speed, accurate POS terminals in the early 90's. You could basically toss products across the sensor non-stop without any delay as long as the code was within view. The modern stuff is glacially slow by comparison.
I also just noticed the dual-conveyor model in operation at a newly-opened Lidl near me yesterday. ALDI here typically doesn't do that--most stores are set up to place groceries (and unfilled bags) directly into a customer cart, and have a nearby counter to bag your groceries at.