Metal leaders are to keep large fish from biting through the line. There are also leaders for changing hooks, and when the main line has a quality of action due to diameter, taper, stiffness etc. Floats are just that. Fishing is done in 3 basic zones; bottom, mid water and surface. The float acts to suspend the hook at a set depth, and also as a visual indicator of a strike. Wood, a sealed 35MM film can and the cork from a wine bottle are a few improvised floats.I will cover this, and more when my report is complete.