Not just practical, S-Expressions are a big part of Lisp's superpowers from a UI perspective. You can manipulate code as forms, not text. It's hard to overstate

Not just practical, S-Expressions are a big part of Lisp's superpowers from a UI perspective. You can manipulate code as forms, not text. It's hard to overstate how much of an advantage that brings to a well-configured editor. When you start thinking of your program as a nested data structure instead of a text document, you start thinking more clearly - you can manipulate this tree representation directly. This makes molding your program significantly faster, closer to the speed of thought. Wholesale refactoring a function might only take a dozen keystrokes to move the forms (not the chars) around. I have a hard time going back to the syntactic busywork of manually placing ascii characters like a caveman.