Earlier this week, Chipotle had a one-day buy-one-get-one-free special to promote their new-ish (and hugely unpopular) tofu tacos. Critics have been taking down the "free"-ness of this promotion in two ways: One, claiming the free burrito requires saving the receipt and—much like a coupon—many will inevitably get lost in bags, eaten by dogs, or thrown away accidentally. Secondly, critics say, the crowds during free-food promotions will make waiting in line not worth it simply due to opportunity cost.

Waiting puts into serious question just how much a person values their time. But just because a person is willing to wait in line, does that really mean they don't value their time? Not necessarily. Some queues are inevitable (such as at the doctor's office), others annoying (the drug store), and some are volunteered for (Chipotle). The amount of time Americans spend waiting in line each year is roughly 37 billion hours. For businesses, queues are double-edged swords: Long wait times can frustrate customers, but they can also enhance the reputation of a shop—especially if that shop is a restaurant.

These two divergent qualities of lines have led shops to adopt different approaches to dealing with them. For shops where customers are not happy in line, distraction is best. One study showed that a shopper's inclination to abandon a line altogether is affected by the number of lines and distractions. Retailers often do this by offering impulse-buy products so customers can browse and continue shopping while in line, or offering entertainment such as music or a screen to watch. And now that mobile screens are in many customer's pocket, free wi-fi can make waits, such as those for flight delays, more tolerable. There's also the traditional way of reducing the pain of lines: temporarily increase tellers or cashiers during busy times.

But long lines aren't always unproductive: Some waits increase the appeal of a product. Behavioral science professor Ayelet Fishbach's research found that waiting for something increases its value, and that these increases can cause people to be more patient. In other words, it makes something "worth waiting for." Restaurants that don't take reservations have made "waiting culture" a signal of quality, and patrons end up valuing their food more than their leisure time. This value, one of reputation, is very important to some businesses. Otherwise, they'd just raise their prices. But hiking prices, and killing the flashing "we're popular" sign, can reduce the customer base.

As for the question of whether waiting in line is worth it: It depends. Since the actual wait itself can feel shorter (or longer) depending on environmental and psychological factors, it comes down to each person's individual preferences whether a product or service worth the wait. The free-burrito promotion at Chipotle was so popular that some restaurants sold out, and lots of people say yes to waiting every night of the week at Manhattan's most popular restaurants.

Economists will continue to bemoan the inefficiency of waiting in line, and come up with efficient solutions that, while wildly innovative, no one will find fair—such as Steven Landsburg's proposal of having new arrivals to lines be at the front instead of the back to reduce wait times and reduce line size (people at the back would give up and leave). And if there's really no happiness to be found waiting in any line, there's also the option of paying someone to wait in line as a line-placement market now exists. But one experiment, which involved paying to cut in line, would suggest that people don't think that's quite fair either.