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With the Sony boasting about how the PS5's SSDs are going to be fast enough to eliminate loading, now might be a good time to talk about the natural opportunities in games to put the kettle on.
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Load times at the moment are in a state I'd consider fairly medium. 15-30 seconds being a fairly bad case scenario, and in open-world games mostly only happening during fast travel since travel. Slower than a couple of seconds, as old cartridges typically took, and an absolute breeze - if one that's more frequent - compared to the screeching with pretty colours of cassette-based systems like the c64. Still, cassettes did have some advantages - No hour or so waiting to install or download patches, patches when you first boot up a game, once it was loaded the game didn't pause to buffer more content in. Just 3-5 minutes of a computer screaming code at you as it read it and you were done. Compared to those modern games that have a lot of loading? That can work out quicker, and it was easier to plan around it.
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Until 2015, Namco had a patent on loading minigames while loading games, at least for optical disc-based media. The idea of loading a small game while waiting for the rest to load has, however, existed since at least Richard Aplin's Invade-a-Load in 1987. While most games used for such purposes aren't historically significant, or if they were aren't significant in that context, I can think of a lot worse things to do while waiting for a game to load than playing a throwaway minigame or port of an old arcade title.
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Some interesting techniques have been used to hide loading over the years - Mass Effect's very slow elevators, Resident Evil's door opening animations, boost mechanics, tight rock formations to squeeze through, and so forth. The first I recall encountering was the wall of fire in Sonic 3 used to hide the transition between the tilesets in Angel Island Act 1 for the zone normally and the zone being on fire. Cartridge based media.
The one that still impresses me is in Metroid Prime. By dividing the world into rooms, not dissimilar from those in the franchise's 2d roots, and having the player shoot the doors to open them the game was able to load the adjacent rooms to the one you were currently in before it needed them. This lead to a gameplay experience that felt relatively seamless, but did have some geometric compromises. Due to how much could be in memory at once, large rooms couldn't be adjacent to other large rooms, and there are some places where this shows - winding corridors with very sparse content sometimes existed purely to act as a loading buffer you couldn't shoot the other end of when you entered. It also experienced some hiccups if you were able to reach a door faster than the game could load the room behind it.
All of these aspects that have become associated with loading will still be possible if the promise of the PS5's near-instant loading comes to fruition, of course, but they'll be able to be timed for exactly as long as the gameplay sequence benefits from it, rather than needing to be inserted for reasons. I for one will not mourn the loss of this aspect of loading.
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Warmup and practice rooms are other things that have come out of loading screens. This has more of a negative if lost since without loading there won't necessarily be anywhere convenient to put them outside of their own modes that, however much I find warmup rooms useful - and sometimes continue with even after loading has finished in the background - I rarely bother opening up dedicated modes for.
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