You can't transfer or pay cash in an instant. When you are using cash, it goes through a ling process especially when your transaction is abroad. With Bitcoin, you can transfer money anytime and anywhere without hassle.
that is right, actually although we are preferring cash right now and not cash but that does not mean that if someone will give money/bitcoin to us we will gonna surely choose bitcoin over fiat and will use that bitcoin in our future or for our daily expenses.