Answer:
Nutrional fact is mention per serving because in a package could be more than one serving, so if you calculate the total calories of the package, you practically will eat anything.
Step-by-step explanation:
The pros is to be learn how many calories each product give us and learn how to combine food or the quantities of each food. The cons is that you need to do some math to know the quantities.
Learn how to calculate the calories of each food, should be realistic of how many calories we need to consume every day.
In a diet, is necessary different ingredients like for example saturated food, but in small quantities, otherwise your body will fill either with carbs, or fats or vitamins.
Remember that every day you need to consume 60 % of carbs, 30% of proteins and just 10 % of fats.
Hope this info is useful.