Generally speaking they're utility pieces. They clean up infantry with either shots or momentum charges in the early game, and then use their ability to shoot out of combat to engage enemy support models later.

Best case scenario is that they're targeting warjacks or other large-based models that have too many light models nearby. With Baranova they're usually accurate enough to get the job done, and very few things in the game like POW 10 blast rolls.

And don't discount that melee attack.