"Look at all this amazing stuff our engine can do!*"
*Probably demoed on PC and won't be in the final version of the game because once we add AI, characters, interaction and all that other stuff that makes a game the PS4 couldn't handle it.
The clouds take 2ms of render time on the PS4. This is from a SIGGRAPH presentation, not a marketing project. Besides, Guerrilla has been very good about accurately showing footage of their games this gen.