Trying to understand something

What difference does it make whether one believes in the doctrine of "consubstantiation" or "transubstantiation"? Yes, I know the former has been condemned as heresy since the Lateran Council of 1215. That's not what I'm asking. I'm asking why we had to settle on one or the other in the first palce. This argument seems to me to be very much akin to different understandings of the Atonement, which on the whole do not diverge into "orthodoxy" and "heresy." A person who believes in consubstantiation believes in the True Presence, as does a transubstantiationist. Both admit that Christ is present in the Eucharist, and both thereby require one to approach it as more than just "a symbol." The remainder seems to me one of those "faith" versus "works" argument that somewhere down the line we are going to decide isn't really much of an argument. We'll say something like "What St. Thomas called 'accidents' Luther called 'material' but both agreed that receiving the Eucharist really involved receiving a physical part of Jesus."

Can anyone shed any light on what substantive, doctrinal difference it makes?