Firstly, it is a government requirement that all large corporations have some kind of sponsorship scheme, be it in sports or charity or whatever. Yes is has tax benefits, if you will point a finger at that, point one to everyone large corp.
Secondly, most of the sponsoring goes from the Nedbank Sports Affinity, which is peoples CHOICE to have a portion of the service fees go to the sponsoring and maintaining for sports events and sports charity's, just like the Wildlife Fund gives people a CHOICE to have a portion of their service fees go to wildlife options. The Golf Challenge is not entirely funded by the sports fund, it is LARGELY funded by advertising and other things like entrance fees, player fees etc.etc
And Nedbank has often been shown to have lower fees in many transactional environments.