Why does it add more calories after I log my exercise?

Say for example, your caloric goal is 1,200 calories per day. If you burn 200 calories exercising, you will have allowed yourself an additional 200 calories to consume. By burning 200 calories through exercise, that would bring your net calories down to only 1,000. Your NET calories still need to be maintained during the day. So whatever you burn off in exercise, you have to make up for. If you don't, there is a possibility your body could go into starvation mode- which is never good. Your weight will drop by doing this, however, it will not be unwanted fat, but rather lean muscle mass. Does that make sense?

This is a huge point of contention on MFP -- use the search tab to search "should I eat my exercise calories" and you'll find a wealth of discussion about this topic. Personally, I say YES! Eat your exercise calories! Maybe not all of them all the time, but your body needs fuel to go and if you're exercising it needs MORE fuel.

You are supposed to eat your exercise calories. However, I have better results when I don't, unless it was really intense and I'm starving later.

My suggestion would be to go two weeks eating your exercise calories, and two weeks without, and see which gives you better results.

The reason it's better if I don't, I think, is because I don't do anything hardcore. If you work out a lot, it's probably a better idea to eat those extra calories.

Those added calories are called "exercise calories." (i THINK that's what they're called.) Yes, it's recommended to eat at least half of them back. This way, if you set your daily calorie goal at 1500 and then you burn 500 calories during a workout that day and don't eat them back, you will technically only be eating 1000 calories (because you burned the other 500 off) and hence will not have reached your goal of eating 1500 calories that day. So, MFP adds them for you after you log in your exercise. Thats why you keep hearing about those Polar heart rate monitors.....sometimes MFP wont calculate your calories burned, correctly.

When you set your base values in your profile, put down your activity level as your day would be without any exercise, then MFP will tell you what you should consume during the day to lose weight without any exercise. Now, if you do some exercise one day and you know the amount of calories burned, enter them into MFP and it will tell you how many calories you should consume to make up for the extra loss that day. The total calories MFP will tell you to consume will still be at the deficit you set up as part of your weight loss goals.

MFP base values are quite ballpark however and you need to experiment a bit to find what suits your body and lifestyle. And don't get overly hung up on it, if you do an unschedualed workout late in the evening and suddenly MFP tells you you need to consume an extra 1200 calories, eat a normal meal, as long as it doesn't happen every day, your body is probably equipped to handle it just fine.