As far as I can remember it goes something like this: Diet and cardio will always shed fat due to the fact that you're A)consuming less calories than your body burns at rest and B) increasing the number of calories you burn when you do cardio. The problem with a calorie deficit and cardio alone is that you may lose muscle mass but increase the definition to your muscles.
If you think about steroids like test, anavar, tren, winstrol what do they do to your body? For sure, they harden your muscles. Tren will increase your vascularity, harden your muscles, and also help you build lean muscle. Same with winny and var. But they also allow your body to recover much quicker than you would be able to without them. So when you add them to the mix (Juice, Diet, and Cardio) you speed up the results exponentially due to the fact that you're body is able to recover quicker. I forget how this goes exactly but building lean muscle helps burn fat quicker (I cannot remember why exactly).
One thing I am now realizing is that if you can figure out how many calories your body burns at rest (Basal Metabolic Rate) you can tweek your diet so you're maintaining your current weight. This will increase your muscle mass, help you burn fat but you won't actually lose/gain any weight. At least, that's what's happening to me currently.
Im sure the gurus will chime in to shed more light but hope this helps some.