Despite its status as an early non-RPG with a save system, JF!'s save system is quick and convenient. I ask everyone to recall the awkwardness of several early save systems, like Crash Bandicoot's.
IIRC, there was a constant stream of free passwords, while bonus round completion acted as a prerequisite for saving one's game. For the life of me, I don't know why we couldn't just save during the CB world map. Also, why have the progress-saving relic known as the password system, when there is a save system?
It's as though Naughty Dog wanted us to maintain our progress, but not too conveniently, if the proper price wasn't paid. Passing through a stage didn't cover that price.