How important were the Japanese carriers to the Imperial Japanese Navy?

Before the USA got involved in World War II, Japan had one of the largest and most modern carrier fleets in the world. However, they were also constructing the Shinano, and had already constructed the world’s two largest battleships, the Yamato and the Musashi. Were the carriers more of a “cool side-project”, a “just-in-case since everyone else is doing them”, or foresight on the importance of carriers in the future on the part on the IJN?