Flyman35....Every aircraft has a minimum weight certified. You would have to increase your take off weight (mass) if you were below the "minimum weight" for the type in question.
Look in FCOM 3.0.1.20 (limitations). It depends on the msn, but 37,230Kg is the minimum for our A320. As empty DOM is typically around 43,000Kg it won't be necessary to increase your take of weight to achieve the minimum required mass. But on some other type of aircraft, if you have no passengers or freight you would have to increase the mass, by whatever means necessary (fuel is the simplest way) to achieve the "minimum weight" for your msn specific aircraft type.
Scally.