tman said:
Cash Purchase, UNLESS you can use the capital amount to create an income for yourself (in a business venture) that exceeds the interest on the car repayments.
Simple as that.
This. If you have cash, it ends up being a capital allocation question. So, you need to look at all the options of how you can allocate that capital, and the respective interest paid or earned in each situation.
If you buy the car cash, you don't have to pay interest on a financed amount, but then you can't deploy that capital elsewhere because it has been used to pay for the car. Depreciation should equally be a consideration, but that is to do with capital preservation, rather than the opportunity cost of financing vs paying cash in terms of interest paid or interest earned.
As has already been mentioned, in the above hypothetical situation described by OP, it's only worth financing a car, if you can use the capital amount (R600k) and invest it elsewhere to get a return that exceeds the interest you will be paying on the financed capital amount use to pay for the car.
An oversimplified illustration that has already been alluded to by others: Depreciation notwithstanding, if you finance a R600k purchase @ 5% interest rate, and could invest R600k in an asset class where you could expect 10% return, then all things being equal, it's better to finance the car and pay it off monthly while your R600k earns a healthy yield. This is a highly unusual situation, as in most cases in real life, the interest in financing a car is quite high, and its difficult to get a higher rate of return (relative to the cost of financing) on capital without incurring a fair amount of risk - which is a whole separate discussion which involves your personal risk and liquidity preferences.
Personally, i stay as far away from debt as possible. Buying a house is perhaps the most justifiable case to raise debt, but I purchase all my cars cash because invariably financing it costs me a lot more money, and I lose out on being able ot invest that money I pay in interest elsewhere (opportunity cost).
The above is my interpretation the hypothetical situation described by the original poster, and should
not be considered financial advice.