The good: Possibly the single biggest thing you can do if you want to figure out why you’re not losing weight. It’ll probably shock you but once you do it’ll be dietary enlightenment.
The bad: Even with apps making it simple it’s still a hassle and a pain. 100% accuracy is also impossible. Calorie counts on products are notoriously inaccurate, there’s individual variance on how you actually absorb food and how you prepare food can change the numbers too.
The stupid: If you’re basing your food choices solely on maths calculation chances are it’s not a healthy approach. Caloric neurosis can set in and it can become a more stressful approach than others, if you're that type of person it mightn't be for you.