Depends on what the paid option offers, of course. In the case of Lispworks it has (as mentioned elsewhere in the thread) a "tree shaker" that makes building s

Depends on what the paid option offers, of course. In the case of Lispworks it has (as mentioned elsewhere in the thread) a "tree shaker" that makes building stand alone apps a lot nicer than SBCL. It also has a superior debugger. I'm sure there is more but these are what stood out to me when I evaluated it (I currently use SBCL almost exclusively, but I can see why someone would pay for Lispworks).