Use redirect_to when you want the browser to receive a 302 redirect
response and go to another URL. Use render when you don't need the
browser to issue another request, but can render a page and return a
200. Examples:
- User fills in form in new action
- Fields are filled in incompletely or incorrectly
- Post goes to the create action, which understands that and renders
the 'new' template again with a 200 so the user can fix errors
- User fills in form in new action
- Fields are filled in correctly
- Post goes to create and information is successfully added to the
database
- You issue a redirect to the index page (or something)