You've been told that your weight depends on just how many calories you consume. So naturally, you think if you're not hungry, you may as well skip your afternoon snack, thereby conserving calories and perhaps losing a fraction of an ounce.
But the math doesn't add up the way you think it does. The only reason you don't feel as if you're starving right now is because you're eating the right foods, spaced out over the right amount of time. That's precisely how the body is suppoed to work and why mini-meals versus big meals are more successful. If you skip a meal or snack and go, say, seven hours without any nutrients, you will quickly lose your equilibrium. You'll once again be ravenously hungry. You'll once again scarf up everything in sight.
And then you'll get depressed. So you'll embark on another day's worth of self-defeating binge-eating and wonder where you went wrong.
You went wrong the moment you decided to skip your afternoon snack, eat a too tiny lunch, or run out the door without planning your day.
Let's do the math. If you skip eating that small apple and an ounce of low-fat cheese, you will have saved maybe 120 calories. However, you're much more likely to overeat later and then (out of guilt) binge all day tomorrow, consuming hundreds or thousands more calories than 120.
Now go eat that snack!