Any yeast will wind up doing the same thing, be it champagne, wine, beer, or bread yeast. It will eat sugar.. and what was the rest revvy says. Pee alcohol and fart co2?
If you use yeast, you're pretty much aiming to halt the yeast once you acheive the desired amount of carbonation, usually by chilling it, pasturizing it, or drinking it as fast as possible. This would thereby limit the actual amount of alcohol produced. (Lets say a full 10 ounces of sugar turning into co2 and alcohol, and divide that small amount of alcohol by 5 gallons of water, it should be negligible but will have a "grown up taste".)
If you let the yeast keep going, then it can, and will, continue to consume sugar and produce alcohol and more co2. That's when you get to the danger point of it being alcoholic beverages.
I prefer force carbing cause I'm a lazy so-n-so, and I like shaking a 2 liter bottle for a minute when I want something fizzy to drink, and then add the soda syrup.