Balanced But Not Fully Balanced

I own a preamp which has both balanced and single ended jacks. I assumed that since I was using the balanced jacks I was getting the benefit of a balanced circuit. I have just now realized that just having balanced plug-ins doesn't mean your preamp (or any other component) is "balanced." Just wondering what sonic compromises are being made with equipment which has balanced inputs and outputs but changes the signal to single ended as it passes through it. If you are using the balanced outputs, what good is that if the signal going into this jack is single ended? I don't understand what good is it to offer equipment with balanced capability only to revert to single ended signals. Is this just a gimmick to sell equipment or is there some advantage to not making the circuitry "fully balanced?"