As a part of production code, I agree, redefining a class is a bad idea. However it absolutely shines during development. I am working as a professional lisp pr

As a part of production code, I agree, redefining a class is a bad idea. However it absolutely shines during development. I am working as a professional lisp programmer, and it is a very common case that I want to add a slot to one of my classes. Being able to do that without having to restart the software in development is very nice as you are not distracted in your programming work by the distraction of restarting.