The boy being described in "Out, Out" is doing a man's work - using the buzz-saw to cut wood for the fire. The saw is helping with this hard work because it is powerful and strong, capable of assisting the youngster in accomplishing this task that is apparently beyond his physical capacity. The saw "ran light" when the cutting was easy but "snarled and rattled" and kept on cutting when it "had to bear a load."
At the same time, the saw is creating the "sweet-scented" smell of the saw dust, and is allowing the boy to spend time outdoors in the beauty of the mountain range and the Vermont sunset.
And, ironically, the saw is ready to agree with the boy and stop cutting wood as soon as "Supper" is announced. The saw "seemed to leap" out of the boy's hand "to prove saws know what supper meant." Most friends would be ready to support a peer in ending the hard work of the day - particularly young men ready to eat a hearty supper after their exertions.