Backbone tries to provide the barest useful essentials -- the main business of building your app is up to you.
I personally prefer minimal frameworks because they don't assume what your finished product will look like. You can grow the application organically rather than trying to fit it into some prototypical mold. Full-fledged frameworks have their uses - they are perfect for getting up and running on known problems. But if you are trying to bake things into an already mature code base or trying a totally different style of architecture, they are not worth the work.
I personally prefer minimal frameworks because they don't assume what your finished product will look like. You can grow the application organically rather than trying to fit it into some prototypical mold. Full-fledged frameworks have their uses - they are perfect for getting up and running on known problems. But if you are trying to bake things into an already mature code base or trying a totally different style of architecture, they are not worth the work.