It's fun for me. This is a good enough reason to do anything.
I learn a lot about how LLMs work and how to work with them.
I can also ask my dumbest questions to a local model and get a response faster, without burning tokens that count towards usage limits on the hosted services I use for actual work.
Definitely a hobby-category activity though, don't feel you're missing out on some big advantage (yet, anyway) unless you feel a great desire to set fire to thousands of dollars in exchange for spending your evenings untangling CUDA driver issues and wondering if that weird smell is your GPU melting. Some people are into that sort of thing, though.