[Touche]

That really depends. If I'm writing a small module that others will use, there's no reason to build that. Or I might just be experimenting with some new browser API.

It's nice to be able to just start coding without the friction of setting up every project as though it were some large thing that would include production builds, automated tests, and many other developers. Of course you can work on those types of projects with client-side loaders just as easily.

I recommend trying out jspm: http://jspm.io/ It is all about removing the friction that people often have with client-side loaders (I have to maintain another config file, the horror! ;) but is also forward-compatible as it implements the upcoming ES6 module loading stuff. You can use CommonJS, AMD, or ES6, and mix and match the three.