Pro: smaller store so you can get in and out faster.
Con: unless you want the multiple choices of a larger store.
Pro: Bare bones presentation - you aren’t paying for any extra frills. Also, the layout seldom changes, unlike other chains where they are constantly shuffling the layout so you have to search for things and spend more time and money in the store. Aldi doesn’t mind you getting in and out quickly.
Con: Some people like the frills and don’t want to do their own bagging. Yes, that’s something no one seems to have mentioned, you do your own bagging at Aldi. Also, no helpful carry-out service or motorized scooters for the disabled. If you need a scooter you have to bring your own.
Pro: Because Aldi employees are expected to be jacks-of-all-trades they work in all parts of the store, so ask the person stocking snacks about the cheese aisle they can give you a reasonable answer.
Con: If the store gets crowded all staff might be up at the check-outs, so getting help elsewhere might be difficult.
Pro: Generally lower prices, good for stocking up on basics/staples
Con: Fewer varieties of any particular item, can’t find exotic ingredients.
Pro: These days, they are trying to expand their produce and healthy selections.
Con: Some stores have issues with their produce. A lot has to do with turnover and how well run the local store is. I’m a regular shopper at Aldi and some stores are immaculate and some are not. In some places the locals buy a lot of produce so it’s usually quite good. In other places the locals don’t buy produce so it sits, which can lead to problems. There seems to be some effort to accommodate local tastes - Aldi in a neighborhood with a lot of Hispanic people will tend to have a larger selection of things like peppers and other related foods. Aldi in a largely polish neighborhood might have more of something else. Produce is also highly seasonal, like it was for everyone 50 years ago.
Here’s how to shop at Aldi: Go there first, and what Aldi has that is on your list buy at Aldi. Then go to another store and get what you can’t get at Aldi. Bring your own bags - you can buy bags there, too, but they were doing the “bring your own bags” thing long before it was trendy. Try their store brand items - in many cases, as others have said, they are the same or even better quality. The “quarter for your cart” thing has already been covered.