I don’t work a lot with clojure but while perhaps, as you say, “businesses may not care about code purity“, consistent behavior of code, a more functional approach, and the ability to reason about what will happen in code can lead to significant increase in speed of development and increased reliability especially for more complex applications, generally. A focus on purity can deliver this. Sometimes getting over the initial learning curve to get to that level is worth it. Sometimes it may not be.