One of the major new features of the PS5 is the next generation solid state storage, and it's also the aspect Cerny spent most time talking about.
Like the Xbox Series X, the PS5 move away from the hard drive based storage of previous generation consoles to fast SSD storage. How fast are we talking about here? Sony claims raw I/O that rewrite the rules of what a PlayStation console can do which makes it roughly 100x faster than the storage on the PS4.
Having storage that fast has a number of advantages. It improves all load times tremendously, which means games launch faster, load faster and also speeds up things like reloading levels or fast travel. In turn this means developers don't need to have things like loading screens or the deceptive long corridors or elevator rides, which are currently necessary to hide the loading time for the next level. Storage this fast could load assets instantly, have seamless transitions, and basically change how games are made.
The faster storage also makes efficient use of the system memory. With the PS4, because the base hard drive was slower, most of the game assets had to be stored on the 8GB GDDR5 memory and would just sit there taking up space. With the PS5, the assets can be streamed in much faster, so only a fraction of the new 16GB GDDR6 memory has to be allocated to the assets.
With the PS5, the entire memory operation from decompression to coherency, mapping, file I/O, and check-in and load management have been updated to work with the faster storage so you get the full benefit of the 100x improvement in memory speed.