It can be used for both.
Using lots of fiber in your diet as a trick isn’t necessarily bad, as long as you’re aware that that’s what you’re doing.
Taking fiber supplements or eating foods that are high in fiber that you don’t really enjoy, are both ways of using fiber as a trick. In essence you are taking something into your body that you don’t really want to, in order to get a desired outcome which is to shed some pounds.
The problem with doing things we don’t really enjoy is that sooner or later we STOP doing them, thereby wasting time and effort and any gains we acquired in the process.
BTW, the reason high-fiber foods can help us lose weight is because they make us feel full. After eating foods like a huge salad or vegetable platter, we don’t feel as much of a pull to eat as much as we usually would afterwards. Fiber also contributes to the feeling of satiety, which has the same effect.
Incorporating fiber into your diet regularly by eating LOTS of it and by looking forward to it (i.e making it tasty) is a way of using it as a tool. Think Caesar salad, melons, berries, avocados etc, all tasty foods that are great eaten alone or with other foods.
Use fiber as one diet tip of many, to get you to eat a little less over a long period of time. The accumulated weight of all that non-eaten food will be visible in what your body isn’t carrying around anymore.
If you do end up eating more fiber, remember that fiber is roughage and water and takes up lots of space. That means you’ll need to start making more room in your shopping cart, car, fridge, pantry and G.I. tract, which can be somewhat inconvenient.
But if that means losing weight, you’ll gladly tolerate that to also have more space in your clothes.