Echo JS 0.11.0

I come from a Rails background, where we have an asset pipeline that's capable combining multiple Javascript files into a single file, which also performs compression and minification on it. Can anybody tell me why I should use something like RequireJS instead of having the server-side asset pipeline combine things for me?

RequireJS with code split up between several sources is good and okay during the development phase. When you go from dev to production you can let r.js combine them for you in order to get your pipeline. 

See: 
http://requirejs.org/docs/optimization.html
and:
http://requirejs.org/docs/node.html

This way you have compiled, minified code that can got into production systems.

Besides, having the server do asset-pipelining during runtime may be unnecessary overhead on the systems circumvented by pre-minification and compression through tools like r.js