Unfortunately, icicles show where hot air is escaping from the house. In the case you see here, the vaulted ceilings only have 6" of space at the eve end of the vault, so the insulation isn't R-38 there. The heat can escape, especially where the truss is. This can cause problems called "ice dams", where the ice backs up under the shingles and water leaks into the house. Most newer homes have flashing that precludes this, as ours luckily does. Still, while icicles look pretty, it would be nicer not to have them.