What does 'yield resource' in the Devise controllers do?

I was looking through the Devise code and noticed that most of the controllers yield the resource being created. class Devise::RegistrationsController < DeviseController # ... def create build_resource(sign_up_params) resource.save yield resource if block_given? # ... This must be some sort of extendability feature but I don't really get how you would pass a block to to the controller action? Note