As far as I can see light tanks have a potential role if you are strictly resource limited and want to deploy a single player soft attack tank that only uses steel and, if possible, very little steel. This kind of assumes that you have also decided you either can't get enough armour levels to be useful or your enemy is so pitiful your don't need much. In this case light tanks are as good as medium tanks and somewhat cheaper (and faster) so they can performa a useful role. For me this is currently a fairly theoretical point but the argument for this usage is fairly sound, it's just not a mainstream game scenario.