title: form_for and form_tag, when to use which one?
body: <p>I am reading a Rails book and so far it has been using <code>form_for</code> to create the forms. In the new chapter that it is building a login page for users, it is using <code>form_tag</code> instead.
  So I wanted to know when and how we should know which one to use? Is it just a educational thing he has done to also show this <code>form_tag</code> too ? or there are more technical reasons that should be considered? </p>