Every person is different. For me, I would consider catching a glimpse of a boss I haven't seen yet to be a spoiler, for example. I'd like to see it for the first time myself. It's an element of surprise, not knowing what's gonna come next, that forms part of my interest in playing certain games. If I knew where all the moons were hidden in a world in Odyssey, for example, it would be far less fun for me playing the game, since the joy of discovery (that this game is incumbent upon) would be lost. If I saw a full playthrough of this game, and then played it myself, I would have some fun, but it would feel incredibly stale, since I would've already seen everything. The actual platforming isn't enough. I want the challenges the game throws at me as a player to feel surprising and new. If I already know what to expect, it removes the motivation to keep playing and find out. That applies to gameplay as much as it does to story. I as a player don't want to know what gameplay challenges the game is going to throw at me, I want to be surprised when I get there. Surprise is a very big motivator.