Imperative builds are a different mindset - where lein projects feel like a different language which emulates Clojure syntax, boot feels more like a library, and context switching is a favourite HN bugbear. Being able to program a build can be a boon, where otherwise you might've had to rely on the creator of your build tool catering to your special case with an appropriate flag.
In practice, though, I've never created a project with very interesting builds in either tool, I only dabble in Clojure. The test will ultimately be whether the community finds it useful.
The biggest thing that grabbed me about boot was the scripting capability. To be able to build concise little applications - 'complete', 'real' applications that can be distributed and deployed - is very freeing. The point of the article was to illustrate how you can get running quickly using that feature and logically evolve into "serious" project-based work as needed.
Ultimately there's more to being productive as a beginner than using the REPL.
