> Not sure in what reasoning one can complain for a method with 25% margin of error (say), but be OK with a method like "5 cakes" which still applies quantification, just in an even more vague and hazy sense.
One method implies rigour and the other one is honest about what it is setting out to do
But you seem to be the only one assuming and/or bringing up rigor in this discussion.
Everybody said it's a quick ballpark figure / back of the envelope style calculation.
The mere fact "cake bad, carrots good" everybody knows. It's not much information concerning "Did I ate too much today?". One can have a caloric budget and stay within it (more or less) without having to be perfect in measurements (or sticking to carrot because it's easier to know its light).
One method implies rigour and the other one is honest about what it is setting out to do