I remove snow off my trees when I feel they are in danger of being permanently damaged. I have eight beautiful Arbor Vitaes in my yard. These trees are evergreen and have a large surface area for the snow to accumulate on. Every time a heavy snow occurs, hundreds of pounds of snow sticks to the branches causing them to bow down several feet till they touch the ground. It makes the trees look horrible and distorts them completely out of shape. As soon as the storm is over and the temp is above freezing I go out with a garden hose and typically spend about an hour hosing off the snow. It takes some time but the trees for the most part return to their normal shape. I suppose if I wasn't around they would probably be fine but I just hate to see them in such pitiful shape.