You know what's fun? Video games. You know what's not fun? Being forced to replay a part of the game you've already beaten. That's why I wish game designers would stop making us do it.
Dark Souls is a game rife with retraversal: most of the boss fights don't have a bonfire (respawn point) near the entrance, so when you die at a boss you go a long way back and must fight your way through a bunch of normal enemies you've already killed before you can try the boss again. Either that or try to run past the mooks, which is often even more dangerous. And while Dark Souls may be an extreme example, it's by no means the only game to make the player replay sections.
I think the reason it's so prominent is because designers look at games like Jedi Knight: Jedi Academy, where you can save literally whenever you want, and rightly see that it causes problems: no fight can ever be difficult because you can just save every time you hit and don't get hit back. They think, as a result, that we have to find a balance between this and going too far back when we die.
But there's a clear line between saving during sections and between sections. It's not just a difference of degree. A "section" should be one self-contained challenge - that is, you start it with full status, and when you finish it, your status is restored. Final Fantasy 13 implements sections and the save system perfectly. Your party is automatically healed between fights, and when you die, you go right back to the field just before you entered the fight, not only preserving your progress in the area but also allowing you to reconfigure your team, equipment, or paradigm deck before trying again, or even give up on the fight and go somewhere else. But you still have to drain the entire enemy group's health bars in one try, so it's not abusable.
Not that every game has to treat individual fights like that. In Call of Duty: Finest Hour, your health doesn't regenerate after each encounter with an enemy, and it doesn't save after each one either. This isn't unfair because the game is balanced so that losing your entire health bar in one encounter is not a credible threat. Instead, they expanded the idea of a "section" to encompass an entire level, or at least a significant portion of it. The challenge of Finest Hour is not simply to win each encounter, but to do so while taking as little damage as possible, so that you can make it to the next checkpoint with your limited health bar. This is also a legitimate way to design action games, provided the checkpoints aren't too far apart.