The goal is to generate regression tests which capture the behaviour of your rails application. Consider regression specs which capture your routes and give you feedback about non reachable routes. A further example where generated regression specs are useful are for inconsistent validations. Consider following validation:
validates :attribute, presence: true, allow_blank: true
A simple spec like:
it {is_expected.to validate_presence_of :attribute} would fail and give you feedback as a developer that your validation is invalid.