according to this site

Yes it is ok and I do it.

I find this a similar program to Weight Watchers activity points. You earn activity points with various workouts and activities throughout your day but you have a choice to eat them or not. Some days, depending on the workouts you will be more hungry. When I miss a workout day and I double up I am more hungry because I burned twice as much so I go over but I rarely eat back all the calories I'm allotted. This gives me a higher deficit. MFP does warn you if you are TOO under your calories, in order to keep you healthy.

I sometimes struggle to eat mine back, but in the end it just makes it easier to up your protein intake.

Sometimes I use these extra calories when I'm actually doing the work out, for e.g when I climb up a mountain I like to take nuts, dried fruit and poweraid drinks to keep me going along with a protein bar. Then I'll have a nice big lunch up the top and make my way back down.
This ensures I don't get really hungry on the way up or the way home and pig out on crap.

Other days I use it as 'treat' as such, for e.g on the nights where I may get take out or go out for dinner and feel like treating myself I'll do extra excersice.

I agree with a post from someone above, saying it is simlilar to weight watchers - and I tend to treat pro points and calories the same. Using the same 'If i want cake I need to get off my fat but' train of thought!

It works really well for me, although I have had a few worries that i'm not eating them all back. Past posts on here have told me that its OK, if im hungry eat, if im not dont

Good luck on your journey to loose, maintain, or gain weight!

if i excercize i can eat more calories

i won't but some people might mistake that for an excuse to eat more. does anyone eat more cause of that? is it ok?

Yes, it's okay. That's how MFP was designed. If you eat back your exercise calories you're doing it right and are using MFP the way it was indended.

There are other methods that don't include eating your exercise calories back (I follow my own).

it would seem counterproductive to eat back all my calories

This. I agree that if you're hungry, you can go over your food, to meet your net. But you shouldn't exercise for the purpose of being able to eat more. I've seen people do that and I think it's stupid. I think it's counterproductive to eat back your calories. I never have, and I've lost 44 lbs in 5 months.

First, understand where all the calories you eat go. They fuel four components including:
Resting Metabolic Rate
Thermic effect of food
Non-exercise activity
Exercise activity

MFP is designed for people to lose weight even without exercise. That means it's formula does not include exercise activity, unlike various traditional TDEE calculations. Thus, it treats everyone as if they were non-exercisers. This means that for people who do exercise, a deficit (their exercise calories) is already established before the person fills out any information at all.

Let's say that person burns 500 calories in exercise, then he/she would, by default, start with a 500 calorie deficit before selecting their desired weekly weight loss goal. So an exerciser would have to add both deficits to get their actual total deficit. If the person choose to lose 1 lb per week, MFP subtracts 500 calories from their total daily energy needs. By not eating back any exercise calories, the person is thus assuming a potential 1000 calorie deficit instead of the planned 500.

By working out and eating back my exercise calories, I get a stronger heart, more efficient lungs, denser bones, stronger muscles, and a clear head -- and I get to pack more protein and other important nutrients into a varied diet and have room for a nice sweet treat every day. How exactly is that "counterproductive?"

I usually eat at least 40% of my exercise calories back.

I got fat because I enjoy eating. If exercise earns me calories to eat, then I'm going to do it. Besides, if you exercise and don't eat some back, you usually end up netting below the recommended allowance.

Feeling hungry, tired and depleted of energy sucks.

if i excercize i can eat more calories

i won't but some people might mistake that for an excuse to eat more. does anyone eat more cause of that? is it ok?

Yes, it's okay. That's how MFP was designed. If you eat back your exercise calories you're doing it right and are using MFP the way it was indended.

There are other methods that don't include eating your exercise calories back (I follow my own).

it would seem counterproductive to eat back all my calories

This. I agree that if you're hungry, you can go over your food, to meet your net. But you shouldn't exercise for the purpose of being able to eat more. I've seen people do that and I think it's stupid. I think it's counterproductive to eat back your calories. I never have, and I've lost 44 lbs in 5 months.

This has been covered before. MFP's calculations (via the NEAT method) include a caloric deficit before taking your exercise into account. The site is set up so that you're supposed to eat back your exercise calories and still lose the weight per week (roughly, since natural variations in weight will occur) indicated by the choice you made.

That said, some folks do like to include a small cushion in the amount of calories they eat back, on the basis that both the caloric intake and calorie burns reported are going to be best estimates rather than scientifically exact.