For the moment, there's nothing particularly life-changing about reduced or light products. They can even work against you, cause you to put on even more weight or become addicted to them.
Light versions are sneaky because they don't contain the same ingredients as the original version: they just try and fool your body into thinking they do! But your body won't recognize the ingredients, which still leaves you hungry for what you thought you were eating in the first place...For example, when you eat a fat-free, sugar-free, calorie-free yogurt, you don't really feel like you've eaten one and your body doesn't either. Result: you end up having another!
Additionally, it is thought that if you eat lots of colored, sweetened products containing E-numbers and chemicals, you get used to their sugary taste and you crave them all the more.
At the end of the day, it depends how often and when you eat them.