Around 1988, Taito began implementing a standard level select code into many of their arcade games. The code was not available to normal players, as it requires the use of the Service button, inside the cabinet. Considering the timing required to press Start and Service in quick succession, it may not have been for cabinet owners either, but instead for the developers who had direct access to the hardware and who may have had those special buttons mapped to something more accessible for testing.
Indeed, some games have more than just level selects, including basic map or object editors and viewers. Some menus allow you to select level numbers well beyond what actually exist in the game, loading non-existant game data when selected. Some menus are very plain, while others obviously had some work put into them. Besides the obvious bonus of easily exploring the game levels without so much work, the menus themselves are sometimes a fascinating look at the developer's side of the game.