If WL e-ticket are not automatically cancelled a situation can arise as follows.
--Lets say after chart preparation your e-tkt remained in WL and is not automatically cancelled. Obviously it will show in the chart and u can use this tkt to travel in General coaches or SL coaches by getting berth from the TTE. But in the mean time you can cancel this tkt using your laptop in the train or u can ask somebody else to cancel it for u. Thus u will be travelling free of cost with a valid tkt.