As Seen In: Con Air (1997)
Practically speaking, pounders are used to drive fence posts into the ground. In bombastic, heightened actions movies like Simon West's Con Air, pounders are used to crush bad guys like Cyrus Grissom (John Malkovich). Obviously the second implementation is the best one.
More than just a popcorn flick, Con Air could serve as fair warning to people who work on construction sites like the one that ends up being Grissom's final resting place: Steer clear of guys sporting unattractively long hair (a la Nicolas Cage's character), because if you cross them they'll put those pounders to wrongful use.