Fiber has been one of the top factors in my own weight control. I've been vegan since the mid 90s, but was slowly adding extra pounds each year. I decided to go on an "if it doesn't have fiber, don't eat it" diet a few years back and lost 60 lbs in 6 months. It massively cut down the sugar and oil in my diet and has consistently helped me control my blood sugar.
One thing I learned is that satiety isn't just about the meal you just ate or how full your stomach just got. If your blood sugar spikes, no matter how big a meal you had or if you ate 4000 calories in one sitting, you'll be hungry again in 3 or 4 hours. Eating a high fiber diet, I can just eat one meal a day or even skip a few days of eating without ever feeling the kind of gnawing hunger I used to get within a few hours of having a full meal.
Aside from blood sugar, fiber is also important because high fiber foods, especially ones with any water content, are usually the lowest calorie density foods and you can eat much larger quantities than you can with highly processed foods. You have to be more careful of highly dehydrated ones like whole grain crackers and dried fruit, but they're still far better and harder to abuse than chips & candy.
