There's no real practical use case besides just being a fun hobby project

There are some niche cases where software rendering on the CPU is used nowadays but it's pretty rare

There are a lot of optimizations that could be done to make a CPU renderer faster, but even so I don't think there are many real world use cases

It's much easier to debug. And CPUs are actually fast enough to do real-time rendering of simple scenes. Because writing for the CPU is so different, and so much easier than writing for the GPU, a pure software stack allows you to explore new ideas.

Running it remotely on a cloud instance? Or on any machine without a GPU.