Should you use them?
If you are trying to make some changes to your weight, it’s probably a good idea to step on the scales.
Of course, you do not have to weigh yourself to know that you’re making progress with fat loss, there are plenty of other ways to track progress: your training log, your body circumference measurements, how your clothes fit, photographs, other people’s reactions etc. All of these are very important. And in some cases - if you don’t have a good relationship with the scales, you may not want to use them at all.
However, if your specific goal is weight-related (i.e to lose or put on weight) I strongly recommend weighing yourself. Why? Because it is the most accurate way of tracking your progress towards your goal and also because it is useful to have the most amount of trackable data to work with. This does not necessarily mean that you have to weigh yourself every week nor does it mean that you should become fixated on what the scales say - it is vital that we take the reading for what it is - another way of tracking progress and not indicative of your value.
Fluctuations in weight
If you are going to use the scales to measure your progress, it’s important to understand that it’s perfectly normal for your weight to fluctuate across the week and you really shouldn’t rely on one weigh-in per week. Weight can fluctuate for many different reasons: food intake/volume, sodium intake, carbohydrate intake, alcohol intake, bowel patterns, menstrual cycles, intense exercise, and the list goes on. These things can cause your body to retain water, which is reflected in what the scales say. Sometimes this water retention may mask fat loss or give you a false impression that you have gained more weight than you have.
How to use them
Taking 3 readings a week, first thing in the morning, no clothes on, after going for a wee and before eating or drinking anything, will always give the most accurate data to work with over the long-term. Add the 3 readings together and then divide them by 3. Track this for a number of weeks and you will get a good idea of what is actually happening with your body weight and whether you are losing body-fat.
summary
The scales provide important data but one weigh-in does not provide the full picture of what is happening with your body, and that’s why it’s so important to look at your weekly average weight. It’s common to see large jumps or drops in weight over short periods of time but these are usually reflective of changes in water weight rather than body fat - your body simply cannot burn or store large amounts of body fat that quickly. So if you’re going to use the scales, use them correctly, take a weekly average, and try to see the reading as nothing more than data to be collected. The weight shown on the scales is a measurement of progress, not your value.