It is scanned in and recorded in the students' records. The answers are not graded, just checked off. Empty papers are discarded. This gives me feedback, on a regular basis, about what is going on in the class. It only takes a few minutes to scan enough papers to extract common themes.
Students feel they are being listened to.
An easy one to do is to bring in a clear bowl, a can of diet Coke, and a can of regular Coke. Fill the bowl with water. Diet Coke floats, but regular Coke sinks. This initiates a nice class discussion on buoyancy and the idea that dissolved salts in water can make it denser, so it sinks. You can also pop the can and talk about dissolved CO2 in the liquid, and how a warm Coke spews more fizzy, because it can hold less CO2.