In a medium where completionists have a lot more on their plate than say, hunting down a collector's edition of a movie or a different cover for a famous novel, your average 100%'ing gamer has to try and see every possible thing across a few hundred hours of play.
That means every side quest, every piece of unlockable armour and every permutation of a given story - even if it means playing through something like The Witcher 3 a handful of times.
There are those goals that require a little extra though; something completely counter-intuitive, and something that none of us really have in mind unless we're thinking like a completionist: Intentionally dying at some point in the story, in order to see some specific hidden scene.
Yes, there are stories where the main character dies anyway, but in addition, those where you can pop your clogs only to unlock a greater sense of finality, are insanely memorable.
-- SPOILERS within --