What you're calling an "open edge", we call in my office a "T-Junction". Open edges (corners that aren't welded) are fine, so long as the edges all come back to vertices that have the same location. T-Junctions (a corner on one side of a face, that rests in the middle of another face) IS bad, however. The main reason for…
Max has a way to check for T-Junctions, its found in the Viewport Options drop down under Xview. It really does help to keep these kind of these tiddy and sometimes you forget about them or don't even realize they are there until later, thats where things like Xview come into play. I think Maya has something similar.