When it comes to the file size of games, it is one of the most important metrics due to the restricted SSD spaces and in this category, PS5 is the clear winner over PS4.
We have often heard about how the file size of games is optimized on the PS5 so they are smaller than the PS4. This was the case recently with Terminator Resistance Enhanced and Subnautica. It also applies to the Xbox Series X, which has generally a higher file size on PS5 aside from in rare cases.
Thanks to the research done by a user on reddit, we have a list of games that show the difference between the file size on the PS5 and PS4.
Now for some clarification on the file size. The user who shared this comparison confirmed that the install size mentioned here is without any DLCs. We also have to remember that updates might increase or even decrease the file size in some cases. Lastly, if there is a difference between the file size listed here and on your console, it could be due to different regions = more languages.
Regardless, this list is a good indication of how the PS5 has the advantage in most games when it comes to file size since the SSD space is expensive. The opposite is true as well, but it is rare. As an example, two games are Call of the Sea (11 GB vs 10.2) and Observer: System Redux (10.4 GB vs. 10.3 GB).