I know I won't lose or gain weight if I lift and eat my exact calorie requirement (including the calories burnt during a workout) - but what will happen to my bodyfat percentage? Will no muscle grow and no fat be burnt?
My answer would be that you do not give sufficient information on your diet to tell what will happen to your body either good or bad. Here is why:
I suspect that by controlling your calorie intake and exercising you want to achieve good figure and/or stay fit and healthy which is great.
Sure your body needs a daily source of energy which is provided by each of the main so called macronutrient classes: protein (4 calorie/g), fat (9 calorie/g) and carbohydrate (4 calorie/g). However keep in mind that calorie is simply a unit of energy which applies to food without specifying the actual nutrient class or nutrition value of it. Remember that a healthy diet should balance the relative amount of these macronutrients classes. Balance is needed to meet not only your energy needs for physical and brain activities but also to provide the right amount of constitutive molecular bricks to maintain your body healthy.
Also of high importance are classes of nutrient not directly related to energy. The micronutrients such as vitamins and minerals are required for your body to keep working properly. Remember the story of sailors sailing accross oceans for months suffering from atrocious tooth decay because of lack of vitamin. Vitamins and minerals though sold as chemical supplements occur naturally in meat, dairy products, vegetables and fruit.
An other advantage of consuming fruits and vegetables is they contain fibers. Fibers provide optimal bowel movement which in turn reduce the risk of colorectal cancer.
Other components present in food which have nothing to do with energy should be on the contrary avoided or their intake reasonabily limited. This is the case for salt which excess of consumption has been demonstrated to enhance the risk of heart desease. Moreover a list of undesired chemicals which are added or develop during the making of processed food are also regarded as unhealthy.
As a conclusion do not think of your body as only a calorie burner. Staying healthy and fit is at least in part a matter of nutrition which means you should actively choose the right food to eat. There is a lot of good books written by nutritionists to help you choose based on science.
To me eating healthy can also be guided by common sense. It is reasonable to think that the body we have inherited from our hunter-gatherer ancestors has not been shaped to eat extra sugar- and fat-rich chocolate bars off trees!
You'll lose fat, gain muscle, maybe get heavier because muscle is more dense than fat, look better, become stronger and more able to do things, walk taller, achieve better posture, sleep more soundly, reduce stress, and feel more confident.
With all the hullabaloo about bulking and cutting, people forget that just working out with reasonably constant food intake will improve their lives in a jillion different ways.
Are you going to increase your caloric intake to make up for the calories that you'd burn by working out?
If you have the same level of physical activity but eat the exact amount of calories as required, nothing would happen.
If you increase physical activity and increase the calories to the exact amount, you would gain muscle.
If you increase physical activity and maintain the calories that you average now, you would lose fat.
The problem is, nobody can predict exactly what is required. So then, that's why bodybuilders consume too many calories and gain fat during "bulking". It's better to eat too much than to not eat enough and end up burning muscle as energy. The human body wants to store fat reserves for the winter and times w/o food. It will burn muscle that it decides are not necessary when in times of depleted caloric intake.