Binds the field to a property in the controller and lets Ember handle keeping things updated. In this example a controller is set up with 2 properties 'number' and 'timesTwo'

ember event response

// in the controller
App.NumberController = Ember.ObjectController.extend({
  number: 1,
  timesTwo: function() {
    return Number(this.get('number')) * 2;
  }.property('number') //tells it to treat it as a dynamic property that updates whenever number updates.
});

//in the template
{{input type="text" value=number size=50}} x2 = {{timesTwo}}

//because we are able to bind properties in templates, 
//we don't have to worry about making sure every event updates every 
// field that might be affected.
//You just update the part you want and let Ember handle the rest.