Curious question.

In order to understand the concept of "eating back" calories, you need to understand how MFP is set up and also the basic idea behind calorie deficits.
Obviously when we want to lose weight, we need to create a calories deficit. Ideally you do not want that deficit to be too great as there are a number of issues that can arise from it. So most nutritionists and diet sites will suggest a modest deficit (which depends on how much you have to lose, the more weight the larger the deficit can be).
Most nutritionists and many other weight loss sites/programs figure out your calorie goal by estimating your BMR (basal metabolic rate) - the amount of calories your body needs just to survive - they figure in how active you are. This includes everything from walki to the bathroom, brushing your teeth, your job AND how often/intense you plan to exercise per week. This gives your TDEE (total daily energy expenditure). That number is what you can eat everyday and neither gain or lose weight. They then create an deficit from this, about 500 cals for every pound per week. So if your TDEE is 2000, your weight loss goal would be 1500 for a lb a week. In this case, you dot eat back exercise cals because they are already accounted for.

MFP is designed different. It figures your BMR and your daily life (how active your job is etc) but it does NOT account for exercise. So it takes that number and creates a deficit. So if you eat that number and don't work out you wi lose weight. You are at a deficit.
Now if you exercise, you create a larger deficit. This goes back to not wanting to have too large of a deficit, especially if you are extremely active, so MFP tells you to eat them back. That still leaves you in a deficit.


Honestly, I have done it both ways. If you are accurately estimating your exercise calories, you pretty much end up in the same place.

Also this is the reason why you see people say "my nutritionist told me I shouldn't be eating back my exercise calories". Because they used a different formula that already accounts for exercise.
If they account for exercise, why shouldn't we when using MFP.

Eta - sorry I am on my phone. Typos.