OK, so my situation is as follows. My company subsidises medical aid and Gap Cover is part of the package. I will note that Gap cover is not from Discovery (where the medical aid is from). Our Gap cover premium is R162 per month and yes, there is an annual limit. The annual limit is something like R185k per person per annum, and according to the presenter, this is regulated.
Practical use - co-payments in any hospital procedure. You will easily pay 3 - 4k per event when a "scope" is used. That is not the old timey girlie mag, but includes endoscopes, gastroscopies, colonoscopies, et cetera. Our little one had a kidney procedure earlier this year. Enter "scope" and co-payment. R160 x 12 = R1920 < R6150 (upfront co-payment amount).
Just one more thing - medical expenses are a tax deduction. Gap cover is insurance. So, strictly speaking, R6150 from my pocket is a tax deduction, not to be added back because I got my money back from insurance. Use it, don't use it - your choice.