Counting calories has a dramatic effect because it makes you aware of how much eating is habitual rather than because you need the input. People start eating less without consciously trying to. I've read that calorie counting is the most effective strategy for losing weight, but it is also the strategy people are most resistant to trying because of the perceived hassle. It is a pain for the first few weeks as you go about measuring everything, but once you acquire data on your habitual foods it's not a big deal.