Another big draw to me is that the checkout process is fast and efficient. Take a look at the packaging and you will notice the barcodes are massive to facilitate rapid scanning.
What is super interesting is that Aldi only moved to barcode scanners very late (past 2000). Before that cashiers entered the product codes manually - they knew them for each product and were super fast at it. The conveyor band never stood still, and they were entering codes the same thing it moved. It was super impressive.
A lot of things at Aldi are structured to make work efficient and need for staff minimal. Supposedly they pass the savings onto the customer in the form of lower prices. The staff often don't have a phone to answer either.
You'd be surprised but some people want to call the grocery store and ask questions. Ask if X is in stock, if they can rent a rug doctor, if they can buy propane, if they can go there to pay this or that bill, what hours they're open, do they renew vehicle registration, etc.