One of the major flaws in using a widescreen monitor to play vertical classic games is the wasted screen space.
MAME is able to push graphics to that empty space.
I used a great resource called Mr. Do’s Arcade on Mameworld.info
There is a massive collection of game art that can be dropped into your MAME artwork directory and set inside the program to push digital versions of the old machine’s bezel artwork to the negative space on the screen.
Using this graphic can drastically reduce playable area on the screen if you do not set MAME to display “cropped” graphics.
I personally like using the bezels in cropped mode, just to add that little bit of color and nostalgic artwork to the sidebars of a normally empty screen.
I don’t mind losing a bit of the bezel to the crop.
It’s the small details that really bring the systems together, I advise you to check out the Arcade Artwork project at Mr Do’s Arcade.