GetJigginWithIt

Found this on the internet.
they are designed for japanese ISO fishing. ISO fishing is primarily a style of rock fishing utilising long soft rods (mine is 5.3metres - full graphite only weights 275gms), bobby floats and very light line (4-10 lbs main depending on your rod). The purpose of the lever drag is that it kind of replaces the reverse switch on most threadlines. Y u may ask.
Two main reasons, the first being that this form of fishing relies of tiring the fish out through the long soft rod. However because of the high risk of line breakage whilst on the rocks ISO fishing need a system of a controlled 'free spool' if the fish decides to swim away from the edge e.g. Drummer fishing being a classic example. This allows the angler to play the fish with greater confidence.
Second reason is that the lever allows the angler to release line without having to open the bail arm. Luderick fisherman would recognise this as a great feature especially as it allows you to control the drift of the float more effectively - almost like using a centrepin reel.