Keeping old games playable is only half of preserving them. If you want to go back to an old favourite to see one particular thing — a late level, an ending, the team you finished with — you don't always have thirty hours to play your way back to it. A save puts you there.
And some of what these games hold can't be reached from the cartridge alone any more. Items that needed a second player and a link cable in the same room. Dragon Quest IX's visitors and treasure maps, swapped between consoles over local wireless. Event Pokémon like Mew, handed out at events that ended decades ago. For a lot of that, a save is the only place it still exists.
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