For me the benefit is the security and convenience of having an internationally-accepted payment method that involves spending the banks' money, and so is protected by the chargeback system. The liquidity is also very helpful. It allows you to put your income to work (earning interest) immediately and not have to worry about inter-account transfers more than once a month.
If you get the cheapest card possible, and never owe interest, then it should cost roughly nothing. e.g. at R48/month, if you spend ~R7k, and have your R7k payment waiting in a 7%-interest-bearing account the whole cycle, then the fee is balanced.
Basically if you're prepared to "secure" for yourself the unsecured credit and learn to use the card "properly", I think you'll be glad you have it.