Popocatepetl volcano spews incandescent material as seen from Paso de Cortés on May 23, 2023 in Amecameca, Mexico. The second highest volcano in the country increased its activity while Mexican authorities raised the alert to yellow phase 3. Popocatepetl volcano caused the fall of ashes in different municipalities in Puebla, Estado de Mexico and Mexico City. Mexican army has spread forces as a preventive measure while the 3 levels of government are in coordination to observe the activity of the volcano and the situation in the surroundings. (Photo by Cristopher Rogel Blanquet/Getty Images)

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.

Maj. Matt O'Donnell of Glenelg, MD shields himself from rotor wash as Ospreys carrying the delegation of U.S. Secretary of Defense Leon Panetta leaves on March 14, 2012 at Forward Operating Base Shukvani, Afghanistan. Panetta is also scheduled to meet with President Karzai during his two-day visit to Afghanistan. The trip comes as the Taliban has vowed revenge following this past weekend's killing spree by a U.S. soldier who is accused of killing 16 civilians in Afghanistan. Most of those killed were children and women. (Photo by Scott Olson/Getty Images)

The galactic core of the milky way occupied by two small wooden boats on July 2, 2014, in Isle of Wight, UK. The Milky Way shines in mesmerizing colourful patterns above the Isle of Wight in stunning photographs. Chad Powell used a DSLR camera to capture images of the spectacular constellation above the familiar beach scenes of England's largest island. The 22-year-old, who shot the pictures over a year of stargazing on the island, often stayed up until dawn to catch the most dramatic sky-scapes. Chad, a graphic designer from Ventnor, Isle of Wight, used foregrounds of abandoned theme parks, harbors and lighthouses against the illuminated sky. Minor adjustments were made to bring out the contrast and whites in the images. (Photo by Chad Powell/Barcroft Media)

(From L) Spanish actresses Aixa Villagran, Leticia Dolera and Celia Freijeiro pose on the pink carpet during the closing night of the 2019 Cannes International Series festival Canneseries, at the Palais des festival, in Cannes southern France, on April 10, 2019. (Photo by Valéry Hache/AFP Photo)

The Kung Fu Panda balloon is lifted before the 86th Annual Macy's Thanksgiving Day Parade November 22, 2012 in New York City. Macy's donated tickets and transportation to this year's Thanksgiving Day Parade to 5,000 people from neighborhoods hardest hit by Superstorm Sandy. (Photo by Charles Sykes/Associated Press)

Wrestlers perform at an all female wrestling event in London. England on August 17, 2017. (Photo by Neil Hall/Reuters)

Australia's Jessica Lim competes in the women's nangun final during the 13th World Wushu Championship 2015 at Istora Senayan stadium in Jakarta, November 17, 2015. (Photo by Reuters/Beawiharta)