confused between loading json on routes or on models

Good day ,

Im new at emberjs and im starting to learn how it works,

what is the difference when specifying the json on routes or on models

model: function() {
var url = 'http://ift.tt/1b39EeD';
return Ember.$.getJSON(url).then(function(data) {
  return data.splice(0, 4);
});

},

this is how i call the json on routes , now my problem , what is the used of this function

export default DS.RESTAdapter.extend({});