Fishly, some of us want a higher area of substrate for aesthetic reasons. More of an undulating bottom seems more natural than just flat. Yes, in a shallow tank, you may be intruding on livable space. But in a 55 gallon, there is plenty of vertical space.
SwampGirl, I am also setting up a 55 gallon, and plan on raising a PORTION of my bed to get it closer to the surface for emergent plants. But don't forget, you can also lower the water surface! I am planning to do this also. This will give me an area between the water surface and the lid/lights for emergent plants to grow in the air.