The Pounder is a powerful tank armed with a cannon with a wide area of effect, fulfilling its "Riot" role by easily destroying tightly-packed units. Its shots push lighter units (Pawn/Blitz etc.) away, potentially even knocking them off cliffs.
Its cannon's high "impulse" rating can even cancel other tanks' momentum, stopping them in their tracks.
However, it moves very slowly and is unable to shoot over other units, unlike Brutes, so they should be used in a staggered line whenever possible. They are also highly vulnerable to skirmishers and artillery, and medium tanks outrange and outclass them in head-to-head combat.
That said, it's an ideal defensive fighter for locking down fast and light units, and is incredibly effective at guarding chokepoints.
Build Dragon's Teeth to make your own killzones—trying to push through a tight space guarded by Pounders is suicide.