^ Yup. It's a bit like somebody who buys coffee from the same coffee place every day, and then that coffee place holds a promotion to which after you buy one coffee for four straight days, you get a fifth coffee for free. There's a certain "cost" associated with the free coffee, but to this particular consumer, it is less than if they had had to pay for the fifth day.
Compare to a different customer who perhaps switched their daily routine to go to this coffee shop for the "free" promotion. Then that free coffee would have additional costs tied in with potential additional costs of travel, opportunity cost of their time, potential price differences in this coffee compared to wherever they went for their old coffee, etc.
In this case, Zachmac and I are the first example. Trevenant is the second.
edit: oo, wait, I thought of a simpler example.
Free promotion: free small coffee with purchase of cinnamon bun. Assuming cinnamon buns cost more than a small coffee, compare somebody who buys cinnamon buns every day to somebody who just wants to buy a cinnamon bun to take advantage of the promotion. One person is getting a bonus free coffee that, for them, cost them nothing extra. The other is getting their "free" coffee, but was is worth the cost of the cinnamon bun and additional travel expenses/ whatever?
Or, you know, replace cinnamon buns with Nintendo games and coffee with club Nintendo points.
(I'm a 4th year BBA major, but economics was never really my thing tbh >_> lol)