To over simplify an answer my 'dry line' leaders will be a minimum of one rod length to a maximum of 1.5 rod lengths (two fly set up). Sinking heads/tips usually not more than two foot long. Exception to this might be where you're using a weighted fly along with a sink tip/sinking leader.
As to why the short leader with tips, et. al? An unweighted fly will tend to 'ride up' in the water column (dry line or sinking). This rather defeats the whole point of using a sink tip/sink leader.