Say you have a set of people who can post on your site and you've created a custom post_type called, "Reviews." You want each author to post and for their posts to automatically go into a custom taxonomy of their name.
So you want Mr. Poe to post and have it automatically post into the taxonomy "Mr. Poe"
Yes, there is the "Gravity Forms + Custom Post Types" add on, but that means that people have to do some input themselves. We're talking about having it happen automatically. It isn't really difficult at all.
Simply add this code to your functions.php file then configure it to match your site's information.
Hope this helps!