The main issue is until digital projection came along, most theater chains were incapable of projecting films in the old Academy ratio. I was pretty amazed I saw Singin' In The Rain projected properly a couple years back, as this was in an 80's era mulitplex.

When they ran a 35mm print of The Shining, it was open matte, but zoomed in, with the extra picture information barely visible on the curtains above and below the screen.

Disney theatrical reissues were routinely cropping the likes of Snow White, until Roger Ebert criticized the practice. The print I saw of Pinocchio in the early 90's was windowboxed on the sides in a 1.85 frame. Not sure if the theater forgot to close the curtains a little more to hide the sidebars, as they did Fantasia right.

The recent film The Grand Budapest Hotel used multiple aspect ratios (including 1.33) to represent different eras.