For me, I've always been fascinated with "live programming environments" and that's been the driving force behind me diving into Common Lisp. I've really come to appreciate this way of working: I was recently working on a web-app that talks to a PostgreSQL database. Normally when developing an app that talks to a database, I'll likely poke around and test out some queries using pgAdmin, the command line, etc. In my Common Lisp app however, once I've got a connection-object to the database, I can just write my queries _within_ the running Lisp system and completely remove the need for those other tools. The plus side is that the data I get back is already in a format that Lisp can deal with. The liveness of the Lisp system really allows for "exploratory" programming.