CNN has an interesting article about placebo buttons:

In New York City, only about 100 of the 1,000 crosswalk buttons actually function, confirmed a spokesperson from the city’s Department of Transportation in an email.

The article quotes Harvard psychologist Ellen Langer for the reasoning behind this:

According to Langer, placebo buttons have a net positive effect on our lives, because they give us the illusion of control — and something to do in situations where the alternative would be doing nothing (which explains why people press the elevator call button when it’s already lit). […]

In the case of pedestrian crossings, they may even make us safer by forcing us to pay attention to our surroundings. And ultimately, pressing a button doesn’t require much effort.

The BCC had a similar article a couple of years ago. Press me! The buttons that lie to you also quotes Ellen Langer, because there is nothing new under the sun:

But instead of framing this as an irrational delusion, Langer described the effect as a positive thing. “Feeling you have control over your world is a desirable state,” she explains. When it comes to those deceptive traffic light buttons, Langer says there could be a whole host of reasons why the placebo effect might be counted as a good thing. “Doing something is better than doing nothing, so people believe,” she says. “And when you go to press the button your attention is on the activity at hand. If I’m just standing at the corner I may not even see the light change, or I might only catch the last part of the change, in which case I could put myself in danger.”