Open Matte offers a fascinating "behind-the-scenes" look at what the camera actually captured, but it often comes at the cost of the artistic composition intended for the cinema. For cinephiles, it is an interesting curiosity, but rarely the preferred way to watch a film.
: Since the director didn't intend for the top and bottom to be seen, you might see "dead space" that unbalances the composition.
In traditional filmmaking, directors often compose their shots for a specific widescreen aspect ratio (like 1.85:1 or 2.39:1). However, the physical film or digital sensor often captures a much taller area.