A man wears a sweater covered in Irish themed pins as he stands with thousands of spectators to watch the 254th New York City St. Patrick's Day parade up 5th Avenue in the Manhattan Borough of New York, March 17, 2015. (Photo by Mike Segar/Reuters)

Devotees push the chariot of Rato Machhindranath during the chariot festival at Bungamati in Lalitpur April 22, 2015. Rato Machhindranath is known as the god of rain and both Hindus and Buddhists worship Machhindranath for good rain to prevent drought during the rice harvest season. (Photo by Navesh Chitrakar/Reuters)

Everyone wants to get something for nothing - whether it's a lucky upgrade that means you can turn left when you get on a plane instead or heading off into the economy seats, or even getting a few extra features thrown in for free when you buy a new car.

As some of the sharpest businesses around, no-one understands this quite as well as casinos and that's why they all have a system that they call comps. It's short for "complimentary offers" and these are special treats specially designed to reward you for your loyalty to the casino in question. They're basically bonuses.

This picture taken on January 25, 2015 shows a participant taking part in an ice water challenge in Zhangjiajie, central China's Hunan province. Participants were required to stay in an ice pond, holding an ice block while eating ice-cream with an electric fan blowing at them. (Photo by AFP Photo/Stringer)

Starting on Monday, August 12, Perseid meteors will streak across the summer sky for a couple of nights, offering casual stargazers and serious nighttime photographers a chance to capture a glimpse of the annual meteor shower. Photo: Photographer David Kingham created this composite image from 23 photos on August 12, 2012. (Photo by David Kingham)

A chimpanzee relaxes in the shade at the Safari Park as the popular attraction prepares for the upcoming Jewish festival of Pesach (Passover) on April 14, 2008 in Ramat Gan near Tel Aviv, Israel. (Photo by David Silverman/Getty Images)

Manuela Vargas at a dress rehearsal for “The Tigress of the Flamenco” given by her company at the Vaudeville Theatre, London. (Photo by Dennis Oulds/Central Press/Getty Images). 4th November 1964

A musician from the Rajan Band, Kotla Mubarakpur holds on to a decorated horse as he and others wait prior to performing at a wedding on November 22, 2011 in New Delhi, India. (Photo by Daniel Berehulak/Getty Images)