Don't knock 'em without precautions

KNIGHT RIDDER NEWSPAPERS
So, should you knock those icicles off your eaves or not?
In most cases, you can let them be. Icicles themselves don't cause leaks, so they're really not the problem.
However, if ice has built up heavily along the edge of a roof, removing the icicles will lighten the load a bit, said Mickey Plank of M.R. Plank Roofing Co. You need to do it very, very carefully, though. Icicles and ice dams can be heavy, he said, and there's always the possibility that you might cause hundreds of pounds of ice to come crashing down.
Plank's advice: "Use a big, long stick, stay the heck away and be sure you know where those things are going to fall." If the ice buildup is extensive enough to threaten to bring down your gutters or other parts of your house, call in a professional.