Though I love McDonald’s, I would never recommend them as “the place you should go to enjoy a good burger”. McDonald’s is a thing — a thing that is not quite food — unto itself. (You are not eating chicken, you are eating McNuggets.) But there are a few things they do correctly, and one of those things is dicing the onions on their cheeseburger super tiny-like.
In a world where recipe writers seek to maximise both flavour and/or nutritional value, iceberg lettuce does not garner a lot of attention or praise. Though it may not have the peppery bite of arugula or the vitamin content of kale, shredded iceberg actually dominates as a sandwich green.
This is good for a lot of reasons. For one, it promotes an even distribution of onion. If an onion is confined to its naturally-occurring ring shape, it can only cover so much surface area. If you were to lay out rings of onion so that every part of the patty was topped with an equal amount of onion, you — much like this sentence — would have too much onion.
Dicing the onion into tiny little bits lets you scatter them with precision, adding just the right amount of allium-y bite.
Then there is the matter of slippage. Depending on how your teeth line up in you head, pulling a large piece of topping off of your burger when you take a bite can be an unfortunate side effect of burger-eating. Sometimes these large pieces of onion fall from your teeth and into your cleavage. This cannot happen if the onion is in tiny bits. Case closed.
Other toppings that do better on a burger when chopped into tiny bits are pickles (you can also just use dill relish) and lettuce (large leaves love to slip). Breaking them down this way ensures an even distribution of texture and taste, plus the toppings stay where you put them until you put them in your mouth.
As a fan of controlling exactly what and when things go into my mouth, I consider the extra knife work to be worth the effort.