When checked, this setting hides the widget unless a particular attribute has a certain value. Only boolean and enumeration attributes can be assigned to this purpose.
A practical example would be a web shop in which the user must submit both billing and delivery information. In this case you might not wish to bother the user with a second set of address input fields unless he or she indicates that the billing and delivery address are not the same. You can accomplish this by making the delivery address fields conditionally visible based on the boolean attribute SameBillingAndDeliveryAddress.