A balanced diet is, eat what our body needs. Our body needs protein, carbohydrates and fat at the same time with the true quantities. We should have a balanced diet because it helps us to grow healthily.

It helps your brain to work better and have a retentive memory. You can become stronger against diseases. Your immune system becomes stronger. In short, your life can reach a good quality. It also helps our heart. When you don't eat unhealthy things the probability of having a heart attack or another disease becomes lower. It is the same for all the organs in our body.
It will help your mental health, too. Because you will be so depressed when you are too fat. You will always think and plan about ways to become heathier and fitter. That's why you won't be able to concentrate on the other things you should do. So, your life won't be qualified.  But there is one thing too you should do with having a balanced diet. It is doing exercises regularly.
And if we think about the healthy food, I think it is not all of the balanced diet. It is just a piece of this. And in my opinion, healthy food is not just vegetables or fruits. We can turn unhealthy food into healthy food with true ingredients.  Like a burger. If we make it at home it will be healthier and safer. Or we can eat the healthy versions of the unhealthy food.
Stay healthy!