If you are diligent with them and stick to it, you can lose that weight. If you are lazy and don't follow them, they will fail. I know I have stuck to them, and I have farted around with them. They work better when they are pushed to the max, and you care about them.
Diets that are sustainable absolutely help people lose weight. While fad diets that involve starvation and the elimination of entire food groups are not necessarily a long-term solution, there are ways to diet that do contribute to healthy weight loss. Sustainable diets that involve learning to eat smaller portions or limiting junk food can contribute to a regular caloric intake that is lower than the number of calories burned from daily activity. This is the basic formula for weight loss.
Diets definitely help people lose weight. When you cut the number of calories you take in on a daily basis, you will lose weight. The key is to have a calorie defecit, and dieting is one of the ways of acheiving this. The other is, obviously, to exercise every day.
I think that diets definitely help people lose weight. I think that if somebody wants to lose weight, they need to eat less calories than their bodies burned. If they do not focus on that, then no amount of exercise will help them. People need to maintain a good diet to be healthy.
The key to losing weight is to restrict the amount of food you're consuming. While that's ultimately something someone should implement in their daily lives, a diet can be a "reminder" of sorts for someone to pay attention to what they're consuming. Paying more attention will in turn lead to better food choices, and ultimately to losing pounds.