Do I need to be eating all of the calories that I "earn" through exercise?

[CAGIRL]

I have a question about using MyFitnessPal. When I log my activities into MFP, it adds the calories "earned or burned" to my total calories left for the day. I want to maximize my metabolism and achieve my fitness goals while using both Fitbit and MyFitnessPal. Do I need to be eating all of the calories that I "earn" through exercise, or can I eat some of them and not worry about it, so long as I eat the minimum amount that MyFitnessPal gives me at the start of each day? I want to make sure that I am eating enough. Thanks in advance for your help.

Moderator edit: updated subject for clarity

[Oro]

This is a REALLY good question. I've read on the myfitnesspal forums a post by someone who says you must eat your exercise calories back. I've then read a blog from myfitnesspal that says you shouldn't. Then, I've looked at the calories fitbit says I shoud be eating to loose wait, it's crazy high! There's no way on god's green earth I should be eating that much food to lose weight. This is some new fangled math me thinks, and I'm not convinced at this point that fitbit is on track with how to actually lose weight for me. I'm pretty disappointed with the charge HR so far. Oh well...