I have a bit experience in JavaScript development but I'm quite new in modern development tools such as Yeoman, Grunt or Bower. But I can create webapps with RequireJS, separate logic with Backbone.js and use templating with Handlebars. I am aware of what's going on.
I saw that these tools leads you to concat files, which is great, in my case I want to speak about JavaScript files. I can't understand how it works.
With RequireJS, I can separate files, for example if I'm using Backbone.js, every model, every view can be a file. If my application is big enough, some pages will need some models and some other pages will need some other models. And thanks to RequireJS I can load only the models (I mean the files, then) I need.