The ultimate goal of this plugin is to make working with forms more fun for everyone.
By improving the interaction, it is easier and less annoying for the user to fill out the form and submit it.
By validating form responses before accepting them, we can alert users to their errors before they submit the form.
In addition, since this is a filter and not an action (read more about the difference here) we're also telling Gravity Forms that we'd like to modify the validation result and continuing processing the rest of the validation with those modifications preserved.
When you submit a page on a multi-page form, Gravity Forms will populate some additional info in the $_POST global (read more here if you're unfamiliar with the $_POST).
For example, if you are going to send an email confirmation letter, the email address should be included in the form fields, and it should be an email address that works.
There are two ways to validate your forms: The basic premise of creating form validation is to look for the names of form elements that are required, and if they are empty, display an error message.
To achieve this, it is important that the plugin is actually deployed on websites around the world, so a lot of focus is spent on making it easy for developers – that's you – to use the plugin.