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Whether youre trying to lose weight, counting your macros, or just trying your hand at portion control, you may have wondered if purchasing a food scale could really make a difference in your progress.

Here's how it works: On the back of any packaged food label is the food's serving size. While some packages share measurements in cups or tablespoons, you'll be hard-pressed to find one that doesn't show what a serving size of that food is in grams, or weight.

So, if you weigh your food before you eat it, you can determine exactly how many servings you're eating, as well as how many calories and grams of carbs, protein, and fat you're putting back. (Note: it's important to subtract the weight of whatever bowl you have your cereal in, for example, before you count the calories for three pounds worth of cereal.)

Meanwhile, if you're eating a non-packaged food like chicken or broccoli, you'll have to look online (like on the USDA's food database) to find how many grams are in a serving, and then how many calories and whatnot are in that serving (or however servings you end up eating).

But is it really necessary for weight loss? Registered dietitian Justine Roth, R.D., director of the nutrition department at the New York State Psychiatric Institute, isn't so sure.

“If you're a bodybuilder and you need your calories to be exact, a scale might be helpful to have more accuracy,” Roth says. “If someone feels like [using a scale] is a way to have an accurate sense of what they're eating, and they're in a healthy mindset, then I'm not against it.”

But in Roth's clinical experience, for many clients using a food scale can be counterproductive or even dangerous. (Speed up your progress towards your weight-loss goals with Women's Health's Look Better Naked DVD.)

“I think there's a very small number of people who can do this without becoming obsessive,” she says. Consider all the work that using a food scale involves, and it's easy to see how obsession could be one not-so-fun side effect. Roth, who primarily counsels patients with disordered eating, says that often using a scale can backfire when patients restrict themselves and then binge later.

“There's this idea that losing weight is a perfect science, and really it's not,” she says. “In reality, you can get there without being obsessive. When you're filling your body with natural, good foods, you'll lose weight. If you eat a lot of processed foods and huge portions, you'll gain.”

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Many people, however, insist that a food scale is a better way to ensure accuracy with portion sizes—and they're not wrong. A 2013 study published in the journal Obesity showed that many labels on processed snack foods contained more calories in actuality than it claimed on the package.

“When I had patients who were distrusting of food labels, I was like, yeah, because they're not true,” Roth says. “What are the odds that every food will have an exact ounce or an exact calorie?”

Instead of becoming a “slave to the scale,” Roth suggests to her clients a less-obsessive (and less-accurate) way of portioning food: Using a regular, 10-inch dinner plate as a template, each portion of a meal should take up roughly one-third of the plate and include proteins, starches, and vegetables. Reasonable portion control using these benchmarks is often more psychologically healthy for clients than using scales, according to Roth.

“If you adapt to a healthy lifestyle, then you will see changes,” Roth says. “Unless you're baking, using a scale just isn't necessary.”