There will always be some reflected light from the film itself. Some of this reflected light will in turn be reflected back onto the film by the lens (mostly the rear element, especially if it is uncoated) and other parts of the camera internals. This light should be well scattered and should simply decrease contrast (and appear to open up the shadows on negatives). The extensive blackening on modern cameras is there to increase contrast as much as possible. If you are not struggling for contrast and like the “look” the camera gives, then why bother ?