I heard that SA and Namibia both require carnets. But I am not quite there yet to give first hand accounts on that. However.....
....in my experience through Africa so far (Westcoast down, currently stuck in Congo/Brazza) the carnet has saved me a truckload of hassle that I am happy to be without. Theres enough as it is. Apart from my passport, Ive come to regard my carnet as the most usefull piece of paper in my possesion. Can it be done without? Im sure it can (pending SA and Namib). Im just asking; why would you want to? Consider all the borders you will be crossing and having to pay for a LP. Add them all up and Im sure you will find the carnet the cheaper solution. And easier! But if you limit your travels to west Africa and 4 to 5 countries, then I dont see the need for a carnet either.