It's not just about reducing the download time. Minified JS will parse faster - especially if using a minifier like Closure Compiler that has various heuristics to remove/simplify code.

I couldn't find any decent benchmarks to say exactly how much though. Of course for your 3kb script it's irrelevant, but a large web app may load a few mb of JS in which case it could make a big difference, especially on mobile devices.