Specials are the lowering of a price in order to bring in more clients. In South Africa and the world over, this never fails to bring customers into your store. Group buying websites have large databases of clients and customers who will then see your special and come to try out your product or service.
However, when designing a special, think of what you want to achieve and how you will make those who do arrive loyal. It is one thing to drop your price and make less profit (or a loss) to bring people to your door, but to keep them requires planning form the start.
Another topic worth reading on is discounts, which cover a similar section of group buying.