If they can keep the puck in the opposition end for the time they on thats the most you can ask of your 4th line. Last night they were dogs of war. They hounded the habs creating turnovers.
All the lines were like that, not just one specifically. But yeah, you want your 4th line setting a fast paced tempo on the forecheck and help out on the PK. Offense production is just extra gravy... 10-15 points is pretty standard from a guy playing 8-12 minutes a game so you want to see them doing more of the other things that helps win a hockey game.