Is there "Terms & Conditions" checkboxes in your form? Do you require all checkboxes ticked in gravity forms or at least one checkbox ticked? Set the Checkbox field with "required" attribute will let you do "multiple checkboxes at least one required" but how to do require all checkboxes ticked?
For examples you have "Terms & Conditions" for your users and require them all agreed. If you have our plugin Gravity Forms Blacklist and Custom Validation installed you may do it easily.
To do that you just need three steps:
1. Create a new custom and validation list
2. Add the rule of "Checkbox options must all be checked" to your list
3. Apply the custom validation list to your Gravity forms checkbox field