what is the main fuction of BNB? Just token for getting free airdrops from the exchange? What is the usecase here? I would be appreciated if someone explained in datails
The main usecase of BNB is paying the trading fees with it. When using BNB there is a 50% discount on the trading fees. Thats what makes BNB a great token, because unlike others it is a token with real use case!
And also these BNB tokens are burned every quarter so as the volume decreases the value and price increases

A great idea from the binance team, as the exchange grows so will the pump for BNB! 2018 will be a good year for BNB