It is a bad advice this is recommended for hatchlings not animals that are two years old the animal could be 2000 grams for all you know so that would be overfeeding the animal. (Which means fast, possible fatty liver issue etc)
Same thing people will recommend 10% or 15% rule yet again you can only go by that for hatchlings, animals grow, metabolism changes etc.
So yes it is an advice that is often given but in certain cases only it does not apply to all which is why it cannot be repeated in all circumtances either.