Just look at this McRib promotion.
Notice it says "Last Days For McRib"
Why do you think McDonald's does this?
Because nobody wants to eat McRibs all year round if they are there all year round... it's a big flop if they try it. But their customers want it BAD when it's only around for a limited time.
This is how the human psyche works and the biggest companies know this and capitalize it in order to drive more sales.
Even Apple, "the company that never runs sales", does this during Christmas time with their special financing offers that are "only available until December 24th."
Walmart, Ebay, Amazon... they all do it. Next time you see it, I know you will notice it.
And as far as internet marketing goes... EVERY SINGLE MAJOR PLAYOR in IM uses countdown timers to push as much product as they can. Frank Kern, Eben Pagan, Brendon Burchard, Chris Record... the list goes on. They ALL use them.
Some people like Jeff Walker, the creator of "Product Launch Formula", only sell their product for one week during the entire year... because that's how powerful scarcity is for sales. Jeff has made 8 figures and beyond from the sales of his product that he only sells with a countdown timer attached.
Bottom line: If you're not doing limited-time promotions and using countdown timers to reinforce them... you're missing out on boatloads of cash.