According to the Associate Director for Science, Office of Science and Technology Policy, Executive Office of the U.S. President, Carl Wieman, the answer lies in what happens after the students are polled. STUDENT ENGAGEMENT!
First you must use electronic polling devices to ask questions that promote critical thinking. Pose questions that students can relate to and that connect to their prior knowledge and real experiences.
The key to learning is in the engagement that occurs after polling.
Engage students by displaying the results of the poll and then have small groups of students debate the various multiple-choice answers, then the class as a whole discusses the different answers, and finally the answer is shown and the problem is explained by the teacher.
Student engagement can also be promoted by utilizing the many new forms of technology including simulations, digital media, interactive lessons, probeware, tablets, apps and other online technological resources such as those provided by Thinkfinity.
I see the strength of electronic polling devices in the data that can then be used to differentiate the instruction. Once the data is collected in a spreadsheet it can be used to determine entire class strengths and weaknesses as well as information to better focus individual students. I have used it on practice math exams to determine topics that need the most review for the entrie class. I have also used it to create a "to do" list for students to focus their own review.
The benefit of the personal polling devices is that it also makes the process more fun. The students are still just answering questions, like they would on a test or in a review book, but using the devices makes it fun like a game.
Yes, I agree personal polling devices are a great tool to provide instantaneous formative assessment that can be used to determine where additional instruction should be focused. They do make the process fun and thus can be used to promote engagement, discussions and learning as well.