In Emacs, every key is evaluating some Lisp expression. You are interactively using Emacs Lisp in a funny sort of REPL. Most of the time you just use predefined commands and they do what you want, but if you know there's a whole programming language there, then you'll see opportunities to take advantage of that sometimes, just like how sometimes it's nice to be able to write a for loop or a pipeline at a bash prompt.
Once you get used to that model of using a computer, it feels crippling to use applications that you can't easily program in on the fly. It's the difference between having a full programming language and a bunch of buttons you can press, and it's for something you're going to be doing a lot for a long time.