Leonardo Da Vinci learned things purely out of curiosity. Not all knowledge needs to be useful. It can be pursued for pure pleasure.
Book: Leonardo Da Vinci
We have seen countless luminaries throughout history, yet none quite like Leonardo Da Vinci. He painted the Mona Lisa, and simultaneously produced unsurpassed anatomy drawings, made river diversion plans, opened the still-beating heart of a pig, designed musical instruments, and choreographed pageants.
However, Da Vinci didn't learn the knowledge required to accomplish all these because they are useful. Instead, his thirst for knowledge was driven purely by curiosity. He pursued it because it was fun. Not all learning needs to be useful.
This view from Da Vinci is very different from what I noted before: information is useless if it is not applied to something important or if we will forget it before we have a chance to apply it. There's no correct answer, but my heart certainly leans towards learning just for fun, as evidenced by a wide array of topics in Weekly I/O, from using your nose to breathe and how Bluetooth works to psychics and weed and Kuleshov Effect.