Having switches on the console allows for a little more flexibility. JP Gunstar Heroes has the English ROM on the cartridge but is only compatible in JP and PAL modes (not US). If you start the console in PAL mode but switch it to US after boot then you get English in proper 60hz.
Hmm, good to know. My Genesis is modded to play games from any region (along with over-clocking, and S-video out,) and I might go this route.