A good explanation posted on reddit
The largest impact that the SSD is going to have is on Game and Level design. Currently, and ever since we stopped using cartridges, games have had to be designed with the speed limit of HDDs (and in the past, discs) in mind. You can actually see these limitations while playing a game – All those super long corridors and long elevator rides, they’re there not because the game designer loves corridors and elevators, but because designers are forced to implement them because of the speed limit of HDDs. This is still an abstract explanation, lets see what impact it has on an actual game:
One of the most requested features from fans of the game Horizon Zero Dawn for its sequel is the ability to fly by mounting robots which can fly. However, this simply would not be possible now because the game was designed with the slowness of a HDD in mind. Here’s why it wouldn’t work – Lets consider Meridian, the large and detailed City that’s in the middle of the map and on top of a mesa, with one end being connected to the adjoining hills by long bridges while the other end is connected to the flatlands below by tall elevators. It was surely a creative decision to design a city like that, but it was also a technical one. Because the City is so detailed and large, with a large number of NPCs each with their own dialogue and music, the data for the city cannot exist in system memory at the same time as the data for the rest of the game world. So when you’re walking towards the city the game is dumping all the data for the open world and loading the data for the city, but since HDDs are slow, the bridge has to be longer and the elevators have to be taller to ensure that the game has enough time to load the city. They also have to put in place artificial limits – for example Aloy’s running speed when she is on the bridge is slower than when she is out in the open world and she cannot ride a mount (the game’s controllable robot horses) into the city because it would be too fast (this is also why you cannot ride a horse into Athens in Assassins Creed Odyssey). Similarly, flight cannot be a thing because the game, or rather the HDD, simply cannot keep up with the speed of flight. If you tried to fly into Meridian the game would just get stuck until its all loaded up and that’s something no game dev will allow.
