Saves working shows the developer knows what they're doing. Breaking saves on every other update is laziness.
Where is the origin? When games were much older, back in the arcade days when you had to put in quarters, people got frustrated that their progress would be lost so out of compassion, or wanting to appease the ever growing angry mob, they introduced password saves to record different moments which worked but was tedious. As technology advanced eventually you had chips dedicated to holding save data but since those were pricey there was a limit to 3 slots which was superior to the old way but still restrictive and thus people whined for more save space. Fast forward to today and thanks to the marvels of innovation we now have games that will periodically save for you with almost unlimited save slots because keeping the fans happy tends to be good for business.
So is it a friendly bonus or an evolved necessity? It's not a "bonus" to expect the game to work correctly
This is why Ren'Py has features to default variable so in the event an old save doesn't have them declared it won't bug out, a feature which can be used after an old save is loaded to run an integrity check to make adjustments, and debugging tools which can be used to add error handling procedures.