We recently needed to setup a hefty form with a lot of checkboxes for a client. In our case, the client needed the user to select every single checkbox within each group of checkboxes. The user could do this one-by-one, but with over 100 checkboxes spread across 12 sections, it would definitely take a while.
To simplify, we needed to add a Check All option to the top of the list of each of the checkbox groups. That way the user could simply click and select everything in that group. However, Gravity Forms does not have this function built in, so we needed a solution.