Explained why you'd want to manually bootstrap, added contrasting
example for automatic vs manual methods.

Added examples, explained the reasons why you initialize the whole app
or parts of the page.

this is to enable nicer tests:

 describe('fooSvc', function() {
   var fooSvc;

   beforeEach(inject(function(_fooSvc_) {
     fooSvc = _fooSvc_;
   }));

   it('should do this thing', function() {
     //test fooSvc
   });
 });