This is a cool trick for cutting galvanized sheeting that I learned a month or so ago. I bought some salvaged sheeting from a guy who tears down chicken houses for salvage - he was barely understandable as he was missing half his teeth and mumbled. When he had told me over the phone to bring a pair of tin snips to cut the metal (20 ft sheets), I had my doubts. However, he showed me an awesome time saving trick. Here it is.
First, make a straight cut with your snips; make a line where you want to cut as well.
Grab the tin on one side of the cut. Put your boot on the other side (closer than I've got here). It will provide leverage as you tear the metal.
Now pull up on the metal with your hand. It will tear fairly easily; readjust your foot as you go. You can nudge the tear left and right by angling the metal as you tear. It's harder to explain than do.
This whole process takes just a few seconds. There's no cutting - which means no noise, no hot sparks, and no sharp edges, as the tearing leaves the sheeting much smoother. I'm definately a fan.