@chrisphin I guess I should explain because the end result is a bit neater than "some game gear games do it."
The Sega Game Gear is actually just a portable revision of Sega's previous home console, the Sega Master System, which competed against the NES before the Sega Genesis. Only difference is the resolution, the Game Gear has a screen with a resolution of 160x144, while the SMS ran in a resolution of 256 × 192, however 8 pixels on each side are considered overscan, so 240x192...
@chrisphin 240 is bigger than 160 horizontal resolution, so game gear games usually would adapt the game to work only in a 160 pixel horizontal window. However, the Game Gear itself could run Master System games directly on the hardware by popping in real SMS carts with a converter, so the game gear needed to be able to internally map 240 lines of resolution to 160 lines. In fact, some retail GG games would just be repackaged SMS carts, no cropping internally.