Specials are a lot of work, and can backfire horribly if you don't get it right. Think about the Papa John's 23 cent pizza give away. It was a spur of the moment decision that did not have the logistic support necessary to even come close to meeting demand. There were understaffing issues, customer flow issues, store size issues. There was violence outside some stores, inability to operate anywhere close to normally, and a plethora of pissed off customers who didn't get their cheap pizza (since stores were out of product by about 2pm in nearly all cases). Absolute nightmare.
Another problem is if no one knows about a promotion. Unless you're able to get the word out, either with advertising or relaying directly to a customer ("...and here's your free scone. We're giving them away all week to let you try our new recipe") you'll never be able to accomplish your goals with the promotion. A classic example of this is a local coffee shop I know that offers a significant discount on coffee when you bring your own cup. I had no idea about this until I saw a another customer get the special rate and asked about it. If they're trying to cut down on paper cup use, they're failing pretty hard.
To recap:
- Make your customers--current and potential, depending on the goal of your special--aware of the offer. Make it clear, define it well, and get the word out. A special no one is aware of is not very special.
- Be operationally ready for it. For the love of everything just and righteous, be ready for the increase in demand/volume/product/everything. If the special takes off, you'll anger customers and stress out employees...not good goals for a promo.
The most brilliant special in the world will only hurt your business if the execution isn't dead-on. Don't design a promotion around what you could do, design it around what you can do.