Otherwise you will think your diet stopped working after a while
The reason checking the scale is useful is because they can clue you in on where a given caloric input is taking you, up or down. The details and timeline aren't really relevant, because if you want the gains to stay then that "diet" is your new, permanent, lifestyle.
If you were overweight but stable, a temporary restriction followed by a return to the original diet would suffice, right?
That's where this article is helpful, as it explains how (and how much) weight gain can be expected when you end the temporary restrictions.
The reason going on a fixed deficit (or bulk) will not just endlessly let you lose or gain weight is because when you lose weight, your body starts being able to operate on fewer and fewer calories. Your metabolism might improve, but nowhere near enough to counter this effect. And vice versa when for bulking.
If you have a high tolerance for food repetition, you can even experimentally see this really easily. Lay out a diet for cutting and you can see the scale will gradually trend towards some specific weight with the decreases getting smaller and smaller. And vice versa when bulking, where you'll see initial big gains followed by a leveling out as your body approaches its new equilibrium caloric intake. This is something anybody who's done any e.g. body building can attest to.
So going on a deficit and then going back to eating what you were just means that you're just going to head back to your old weight. So diets really need to be a permanent lifestyle thing, which is why finding one you can be comfortable with is so critical.
> The reason checking the scale is useful is because they can clue you in on where a given caloric input is taking you, up or down.
you could just grab your stomach fat to get a more accurate progress measurement