With Auto Field enable you can create a hidden field that get automatically filled in with the pattern of template tags that you can set by the field settings. This can be very handy when you want te set a field with a combination of field data that is searchable, or just print on your page.
Make sure your system meets the minimum requirements:
For every Auto Field that you create you can set a pattern based on some default template tags that are coming from the entry.
In the example above we using the pattern {entry_id}-{title}. When you save the entry, that Auto Field get also pared and filled in with the current Entry_id and Title.