This is an old article but still relevant, especially since Clojure allows co-mingling Java and Clojure (Lisp) code. I find Clojure especially useful on my own projects because there are no problems finding developers or getting customer approval for using a very nice, but niche language.
I still like (J)Ruby a lot but the runtime performance of Clojure is better and the two languages seem, to me, to be equally "agile" - both are a pleasure to code in.
He is saying that he uses Clojure for personal projects because those are the projects where he doesn't have to recruit for or justify his choice of a niche language.
I'm guessing what he means is that, because Clojure can work so well with Java, he doesn't have to find people with Clojure experience to help on a Clojure project, he can just get Java people (of which there is an abundance).
Getting customer approval is often the hardest part. Back in 2002 I started working with Python and Zope. It was easy to hire and train people in Python and Zope (you can pick up Python in an afternoon and work from there), but it was mindbogglingly hard to convince customers the data not being in a relational database was, actually, an advantage.
I still like (J)Ruby a lot but the runtime performance of Clojure is better and the two languages seem, to me, to be equally "agile" - both are a pleasure to code in.