It softens it and allows more moisture in the bread. The grains become more digestible. It's not as if the texture of cornmeal is lost, but sometimes cornmeal can be unpleasantly gritty. Notice how most cornbread calls for a good amount of white flour. Southern cornbread recipes often call for just cornmeal, and really, they're kind of dry. When you soak cornmeal, you can make a cornbread with all cornmeal and have it be moist and lighter in texture than if you tried to do it without soaking. Same thing with yeast breads, like the anadama, or a bread like broa. Without soaking, you can sometimes get a gritty, raw-tasting texture from the cornmeal (you actually cook a part of the cornmeal and then let it sit for a while for broa). You can still definitely get crunch from cornmeal in these breads.