Overlays are nice but i only use Vectrex Bezels.
All others are just for fun.
On my Bartop, 1280x1024 (5/4), honrizontal games take full screen.
There is no area to draw an Overlay. (or shrink emulator viewport).
But for vertical game (Arcade), an Overlay is nice.
Just one i use with mame games.
For 16:9, some generic Bezels can be a good idea.
Make overlays (Bezels) for most games/most resolutions must be difficult.
I think, Recalbox must propose the possibility to put overlays but trying to do all/most overlays is difficult.
Hum, ok, a nice overlay can be cool...
Some Overlays/Bezels i found :
https://mega.nz/#F!5AJ0XRpL!wcyQdAyzn7GyydK0ONKy-A