Finding just the right spot above the clouds at Camp 1 on Ama Dablam, Danuru Sherpa uses his iPhone to catch up with friends and family. Even at 18,500 feet (5,654 meters), climbers here can check their email and other dispatches from the world below. (Photo by Aaron Huey/National Geographic)

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.

Miss Puerto Rico Stephanie Del Valle (C) reacts after winning in the Grand Final of the Miss World 2016 pageant at the MGM National Harbor December 18, 2016 in Oxon Hill, Maryland. (Photo by Zach Gibson/AFP Photo)

Western lowland gorilla Kijivu holds her newborn baby at the Prague Zoo in the Czech Republic. (Photo by Isifa/Getty Images)

“Centuries ago, Inuit hunted the bowhead whale. At that time, whale hunting undoubtedly was part of a complex and very important ritual, if only because of the size of the catch. The position that the ancestors of today's Inuit occupied in the living world involved a relationship with the spirit that inhabited each animal but also their species”. (Photo by Robert Frechette/2014 Sony World Photography Awards)

Bangladeshi fisherman feed their otters as they catch fish in Narail some 208 kms from Dhaka on March 11, 2014. The fishermen are using a rare technique that relies on coordination between man and trained otters, a centuries-old fishing partnership that has already long died out in other parts of Asia. (Photo by Munir Uz Zaman/AFP Photo)

Iraqis who have fled fighting between security forces and al-Qaida inspired militants in their hometown of Tal Afar arrive in a car at Germawa camp for displaced Iraqis, in a hot dusty plain in the largely-autonomous Kurdish area of Dahuk, 260 miles (430 kilometers) northwest of Baghdad Tuesday, June 17, 2014. (Photo by AP Photo)

Rickshaw drivers wade through a flooded road after heavy rains swept through Guwahati, in the northeastern Indian state of Assam, on June 26, 2014. Seven people have been killed there in flash floods, landslides and heavy rainfall, local media reported Friday. (Photo by Utpal Baruah/Reuters)