I know that the Sega Master system had two primary game formats: cartridges just like the NES and other game consoles of the time and the "Sega Card" which was a 2mm thick plastic card with contact pads on the back making it look sort of like a credit card sized SD card.
These were supposedly cheaper for publishers to distribute games on (though limited to games small enough that they wouldn't require banking/mapper chips) but I'm wondering why that was the case.
From all that I can tell it seems like the cards were just a single 4KB to 32KB rom chip epoxied into a plastic shell. That would remove the extra cost of a circuit board and larger plastic body but compared to the cost of the custom ROM chip it doesn't seem like it would make much of a difference if the game was already small enough to not need a mapper or other special chips.
Were there other differences that made the price difference big enough to justify having a second game slot and special format just for small games?