Dave Navarro, Jr. on "AJAX best practices"

I am coding a plugin that allows logged-in authors to edit data in a widget area on the front-end using AJAX.

I basically have it working, however the example my code is based on (from the Lynda.com tutorials) does not use a NONCE when submitting data from the form to WP using AJAX.

Is a NONCE not necessary when using AJAX? Or is it best practice to always use a NONCE when submitting data?