One common complaint of Clojure REPLs is their startup time. Although that complaint is often somewhat unfounded (and related to tooling), it still takes the bare Clojure JAR about 1 second to start on new hardware. Planck — through bootstrapped ClojureScript, and owing to the small latency exhibited by JavaScript VMs — managed to improve the time that it takes to bootstrap a Clojure(Script) REPL.