Sites like MyFitnessPal and MyNetDiary would likely disagree. They have hundreds of thousands of users. However, I agree that if you're in generally good health then it probably is too high of a burden.

> I know what I shouldn't eat

I'd argue you probably do not know what you should or should not eat. Sure, in general you know you should avoid eating candy for every meal, but I suspect you don't really know which particular ingredients are resulting in a change of your state.

For instance, many people are gluten intolerant for years before realizing it. If you were able to track foods to the approximate level of knowing the level of gluten in your body at a given time, you could identify gluten as a cause of some symptoms. I would also make similar arguments about the long-term effects of certain diets (semi-vegetarian, low-carb, etc.).

I guess there is a divide between the kind of myopic analytic insight you're looking for and the more long-term ones I'm interested in. Both are valuable, but they require different data sources.