Why use this.get('serviceName') instead of this.serviceName?

In Ember.JS, Is there a good reason to be doing this:

import Service, { inject } from '@ember/service';

export default Service.extend({
ajax: inject(),
getAll() {
    return this.get('ajax').request(`api/users/`, {
        method: 'GET',
        contentType: 'application/json'
    });
}
});

As opposed to this?

import Service, { inject } from '@ember/service';

export default Service.extend({
ajax: inject(),
getAll() {
    return this.ajax.request(`api/users/`, {
        method: 'GET',
        contentType: 'application/json'
    });
}
});

The second method looks cleaner IMO, but I'm wondering if there's a good functional reason to be using .get() over just referencing the service directly.