What dose drinking distilled water do for you?

Nothing much, really. Unless you live in an area where the water is undrinkable due to bacteria contamination or salt- it offers you no benefits at all. Distilled water contains no minerals or other impurities, and also has no taste to speak of. Beverage makers will use it in their process as a means of controlling product quality, and batteries use it because pure water is needed for the reaction inside. Humans don't benefit one way or the other, providing the water is drinkable and safe to begin with. There are rare folks with metabolic disorders that do use it, to preclude suffering kidney stones or gout attacks- otherwise normal folks can drink it out of the tap without ill effects. For normal folks, it offers no benefits that would make it worth the extra expense or effort to produce it.