You should if you are trying to lose weight. You can calculate your energy balance and figure out how much to eat each day when you know your number. You need to reach a negative energy balance to lose weight.
To reach a negative energy balance, you need to make sure that you put less energy in your body than your body uses. That means that you need to consume fewer calories than you burn each day. But to do that you need to know how many calories you burn!
Also, you need to combine increased activity and diet changes.
Making small adjustments to both your caloric intake and your physical activity is generally recommended as the most reasonable and sustainable method of weight loss.
Using this method, you can burn a few hundred extra calories with a workout and cut back calories by eliminating dessert or high-calorie snacks to reach your goal. It is also the best way to maintain your weight after you've slimmed down.