Your point about repeatability is valid. As a policy matter we would never advocate building a project without codifying the process as zero-arg tasks in the build.boot file. You can see this in our own projects (eg. https://github.com/tailrecursion/boot-useful/blob/master/bui...). This project has one way to build the project jar file:

    (deftask build-jar
      "Build project jar file."
      []
      (comp (pom) (add-src) (jar) (install)))

When you build the jar file you just do

    boot build-jar

This ensures repeatability, etc.

But we don't only use boot for repeatable builds! Boot is in a unique position in that it's on the intersection of application and environment. That is to say, boot can be used to "bootstrap" the application. With boot we can create sort of self-configuring applications, where the entry point of the application is the build.boot file. This is a very clear win, for example, when running Clojure applications in docker on Elastic Beanstalk, etc. (We'll write that up, too.)