You can use it to collect class student responses, making it a good way to generate group formative data and student questions on a topic. It presents data in visual and interesting ways and is useful for generating lines of inquiry, surfacing misconceptions or creating "hinge questions" for a topic.
NOTE: Free Mentimeter only allows two questions per presentation. This is enough to gather class data on hinge questions or feedback on the topic. If you want individual student data, other tools (including Moodle quizzes) are better.