To clarify, the IP address is the user requesting the form, not your hosting servers IP. Here's how it works:
1) User's navigates to your page and is presented with a legitimate form. This form contains the uniqueId found above.
2) When the user submits the form, the uniqueId is verified.
The reason this works is because if another website has a form linking (and posting) to your server, they now cannot do so since they lack the ability to generate valid unique ID's.
In general you don't need to worry about this, as long as the form data is valid there shouldn't be any concern. However there are times where it is useful. . . I've never needed to though!