I think designing "useless" things is actually a really great exercise that forces you to challenge a lot of your biases/assumptions and really flex your muscle

I think designing "useless" things is actually a really great exercise that forces you to challenge a lot of your biases/assumptions and really flex your muscles. I help teach some people intro-level coding and we practice on "useless" code all the time, like text mangling to do meme-posting, writing some data-moshing tools, etc. It's practical in that it teaches some fundamentals, but the output is ultimately silly but observable. (e.g., there's not much value to the program but a successful output is clear) Useless inventions are pretty fun for a lot of things; theatre/home movies are filled with such things as CG is typically too much work for an individual, so practical effects need to be used. For a movie I made for a friend, we had to figure out how to make a puppet "blow" into a party noise maker, and came up with the strangest contraption involving straws and a lot of tape; a overall "useless" invention, but turns out there's a lot more going into making noise with a party noise maker than you'd imagine. Useless inventions are a great exercise of creativity and logic, blending the practical side of our minds with the emotional/fantastical parts that just want to make such fun and fantastical things work.