calories

The majority seem to say eat all your available calories (exercise and all). I aim to eat all my daily calories, but I try not to eat my exercise cals (I do sometimes, though). It's the deficit that's helped me lose weight.

You eat them all--you have a built in deficit when you set up your profile so when you eat your BASE + your EXERCISE calories you maintain that deficit.

Think of it like this. Person X maintains her weight on 2000 calories because she's lightly active (this doesn't include exercise--just living. Say she's a nurse and walks around at work). She wants to lose 1 pound per week so MFP has her calorie target set at 1500 calories.

If she did no exercise, she would simply eat 1500 calories:

1500 + 0 exercise calories earned for the day = 1500 calorie target. Her deficit is still 500 calories.

Now let's say she's exercised and burned 250 calories doing a 2 mile jog and cool down.

1500 + 250 exercise calories earned for the day = 1750 calorie target.

If she eats 1500 then she is 250 below her NEW target...her deficit is now the original 500 (from simply eating 1500) + 250 burned from exercise = 750.

problem?
some people think it's not a problem--they aim for the maximum deficit possible in order to speed up weight loss. Not a good plan. With too great a deficit you catabolize muscle mass and thereby reduce your metabolic rate and lower your adherence (because being hungry simply sucks). Which is why you eat your "base calories" + "exercise calories" to maintain the original deficit you set out to achieve each day. Your weight loss rate will remain at 1 pound per week and you will reduce the amount of muscle mass that you lose from dieting.

Hope this makes sense.