Oh that's the brilliance of it, once u convert to the smart chain, there is no need for eth at all. Yes BNB id still necessary, however the price of BNB is rising, which makes using it a charm. The main reason to use it is to get familiar with the setups, because this is the way of the future! One day you will be glad you did when the HIVE smart chain comes out you will be that much ahead of the curve!