Hidden Fields

Hidden fields are pretty much self explanatory – they are fields which have a preset value which are not presented to the user.

Imagine you have a situation where you have 2-3 different web sites which all share a Google Form. You’d like to know which site a form response originated from. You could do this with a hidden field. You define the Google Form within each of the three web sites with the hidden field set uniquely for each site. When the user submits for the form, the hidden value will be submitted uniquely identifying the site the form was submitted from.

There many other similar use cases. There is some background information on my web site from back when I first implemented it.

I failed to answer the second part of your question. With respect to Advanced Fields, the only way to do that would be to set it up using a multi-page Google Form which takes a different path through the form based on your responses.

I have an example on my site which takes a different path based on your responses.

There isn’t any sort of fancy Javascript available to show or hide fields based on user response. While it would be technically possible with jQuery, it would be pretty form specific and not something easily built into the plugin in the general case.