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Pop-in essentially exists because the draw distance is too low. As the player get's closer to an object, it is more likely to be drawn, and the level of detail it is drawn at is higher.

While it's not Saturn/PS1 levels in modern games, in very large and very open maps you can have this problem where you know in the distance there can be things that you simply cannot see because of draw distance. If your running towards something in the distance, there can be noticeable 'step-ups' as it decides to draw the model with more and more details. So it comes up in exploring very large and very open areas. This happens to various degrees even on PS5+ level hardware.

There's a similar issues with movement speed, but instead the limit is how quickly can the game load new content.