Why is Common Lisp case insensitive?

Question

Is there an advantage to defining a function like (defun hi () \"Hi!\") and be able to call it by using (hi) or (HI) or (Hi)

Answer 1

By default the reader in CL is case converting, all escaped characters get turned into uppercase. You can customize this behavior with readtable-case. This is because its easy to interface with other languages that follow the same conventions.