> The answer is if you want to lose weight it doesn't matter. You just need to average a deficit over time.

If this were the case, Weight Watchers (which is at its core a calorie limiting system) should have a near 100% success rate. It doesn't. A casual perusal of Google shows closer to a 50% success rate for a 5% body weight change.

I can't think of many medical treatments where we go "yeah, a coin toss level of success is good enough for me."

As for the accuracy of the measurements - it does matter. Healthy weight loss rates are, mathematically, in the 10% calorie reduction range. That's less than the error rate for the caloric labeling of many foods.