There are, however, people who have to seriously avoid certain ingredients, and it is a pain to go through all the fineprint, which is sometimes made quite difficult to read. For example, check the Asian section in your grocery store.
If you are shopping for multiple people in the family, some of which have some restrictions, it is hard to map everything confidently when shopping.
If you are traveling abroad, like Japan for instance, especially with dietary restrictions, an app like this can be quite handy.