Bitcoin is useful as it is fast, safe and cheap. Has very less transaction cost and transfer is fast without any amount limitation. It is digital currency so no need to carry any cash more and can use to by stuffs online. No bank involvement or any other third party. It gives great opportunity to invests money in to make more profit.
Bitcoin is not as cheap as you think. The fees for small transaction is higher than evern and because of that, no one wants to use bitcoin to buy a cup of coffee. The fees are even higher than a coffee and therefore, cheap is not a factor of bitcoin. I think they use bitcoin because it is fast and secure than traditional currency