I don't use one and I have fell when my lower platform slipped and fell about 8' down the tree. I tried to lower myself down to hang from the top part then drop down to the platform but when I started lowering myself from the top piece it tipped and I fell down to the bottom half with my legs slipping through. Hurt like a sun of a beeeouch. Now I keep the two pieces tied together and make sure the pieces are set into the tree before I move up or down, slow methodical movements.