I tend to think of normals as front and back surfaces. Strangely, as you're modeling it is possible to have a section of a surface facing the wrong direction even though the rest of the surface is correct. This will create problems when texturing, converting to other geometry types, or merging with other surfaces.

As for history, once a model is finished you should no longer need the file to "remember" all the steps it took to create the model. Additionally, history may have adverse affects with deformers, skeletons, or other animation actions.