A save prompt after every level makes lives useless and irrelevant.
Having a "save hub" you can save at whenever you want is practically the same thing as an autosave except much more annoying for the player, having to walk over there every time. Making saving have a fee would give it a bit more of a point, but someone could still farm lives then spend time collecting the needed amount of coins with their extra lives, which would then also be the same thing except even more than even more tedium.
Saving only after castles/ghost houses makes it a lot more difficult to save, giving lives a bit of a purpose, but of course there is still possible life-grinding. And if life-grinding isn't an option, getting a game over makes you have to replay levels you've already played, which not only is boring, but also frustrating.
As you can see, the option here that I dislike least is autosaving. Also for those of you complaining about the game automatically saving when you don't want it to, SMW had a "Continue Without Saving" option.
Being able to save at your own leisure is pretty much the same as saving after each level, except making lives
even more useless. And also having to walk over to the tile takes unnecessary extra time. We live in a society with some very impatient people, you know.
The "lives per level" idea is like
combining the tedium of the save hub and the game over.
tl;dr we wouldn't be having this argument if we had gotten rid of lives earlier.
May we meet again outside the battlefield.