It can still be useful just to get rough estimates of what you're making at home, especially for portions and products that are roughly comparable.

If I make an egg, cheese, and sausage sandwich in the morning, and forget to weigh out or count how much of something I used, it can still be useful for back-of-napkin estimates if I Google the McDonalds Sausage McMuffin with Egg.

Obviously it's not going to be exactly equivalent, but I usually assume my homemade thing is 20% more than the restaurant to compensate.

It's of course better if you just weigh everything out first, you can get much more accurate measurements and calorie estimates then, but this can work in a pinch.