how is it used to extend game time?
Seems to me it would be the opposite - it forces you to proceed with the game and as a result finish it sooner, as opposed to someone like me who saves and replays certain parts repeatedly either for fun or getting it right.
Unless the save points are spaced out really far apart, then i guess i could see how that would do it. I dont generally die often enough for that to be too big an issue personally, what with most newer games ive played being easy
Most games that use checkpoints force you to redo sections based on the ancient trial-and-error mindset, which essentially means doing the same content over and over.
Not only is this tedious, it also makes the gameplay sections between points into little separate puzzles instead of a pleasant flowing experience. Because of the checkpoint nature, you will automatically start memorizing patterns, so you can avoid redoing the content because no one likes repetition. It's one of the worst kinds of game design, if you ask me.
Developers know you're used to redoing sections, so they can add much harder trials so you can fail some more - because it's ok to die. To me, it creates a very bad gameplay experience. What they should do instead, is make the challenges solvable by observation and clever thinking. That way, you could avoid dying and redoing stuff by being smart.
They don't have to do this, though, and again - it's because of this "tradition" of trial-and-error.
GTA4 is an excellent recent example, and you can probably count hours of gameplay based on redoing sections.
It's pretty basic, really.
It's also tradition because consoles used to have no harddisk and as such, not a lot of space available for save games.
Finishing sooner because you feel the need to press on has nothing whatsoever to do with the length of the game, so your point is not logical.
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The reason this isn't changed is basically because developers today don't understand game design. They're basing their designs on "proven" concepts and the traditions of the past.
They're not interested in evolving genres or taking things to the next level - they just want to go with what works.
For that, they look to others and not within themselves in an effort to progress the various genres.