Counting calories is a very effective way to lose/gain weight. Sure you don't know *exactly* how many your body is burning, but if you don't lose or gain weight at 3000 calories, and maintain the same lifestyle, you can be sure that you will lose about a pound a week at 2500 calories, or gain a pound a week at 3500 calories/day. Sure not everybody wants to or has to do that, but it works.
When you restrict calories in, the first thing that happens is your body lowers it's energy expenditure by making you tired and lowering non-essential processes in the body. Then it will catabolise muscle, because muscle is more expensive metabolically than fat. Only then will it start to lower fat. You will get to your target weight, but you will have less muscle mass (unhealthy in itself) burning less energy and a body which thinks it's in a state of famine and will drive you to binge eat to increase fat stores whenever food is available. In short you will lose weight but will set yourself up for even more weight gain in the future, or at least a lifetime of chronic stress inducing hunger. This is why 98% of people who do calorie restriction diets fail.