As far as use cases are concerned, I think of Common Lisp as a higher level C with much better ergonomics. My particular use case is prototyping low level computations for performance tuning. Common Lisp excels at prototyping. I guess if you need to implement something for which there already exist 20 other libraries there is not much point, which is also the reason I'm not a huge fan of Rewrite in Rust movement.