exercise vs. no exercise

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When it comes to losing weight does it really matter if you exercise? I know exercising is best for your health, but I'm just curious about weight loss. I usually eat about 1500 calories a day and burn around 300 through aerobics, but on days I don't work out I adjust my calories to eat only 1200. So I'm wondering, in terms of weight loss, does exercise really matter if at the end of the day my net total for calories is 1200?