[foobarbaz33]

With lisp you typically develop in source files, versioned with Git. The same as any other language. Source files and live development are not mutually exclusive. SLIME can send code snippets from your file over to the REPL for live development. You have your cake and eat it too.

The REPL (or scratch buffer) is typically used for testing/observing. Not the actual source code development. Although it is possible to never write your source code to a file if you're just playing around with a toy experiment.