People ride a prototype of a driverless vehicle as it is moves through a pedestrian area in Greenwich, east London, February 11, 2015. Britain has begun testing driverless cars in four cities, launching the first official trials ahead of a series of planned rule reviews to accommodate the new technology. (Photo by Suzanne Plunkett/Reuters)

A hand of a devotee is pictured as she rings a bell while offering prayers to the chariot of God Bhairab during the Bisket festival in Bhaktapur, Nepal, April 13, 2016. During the festival, also regarded as Nepalese New Year, images of the Hindu god Bhairava and his female counterpart Bhadrakali are enshrined in two large chariots and pulled to an open square after which rituals and festivities are performed. (Photo by Navesh Chitrakar/Reuters)

A devotee is smeared with a vermillion powder while celebrating the “Sindoor Jatra” vermillion powder festival at Thimi, in Bhaktapur, Nepal, April 14, 2016. Devotees mark the festival by playing traditional drums, singing, dancing and carrying chariot of various deities around town while throwing vermillion powder to welcome the advent of spring and the New Year. (Photo by Navesh Chitrakar/Reuters)

A deserted alley in the ghost town of Apice, in the province of Benevento, southern Italy, 22 November 2016. After the Irpinia earthquake that took place in southern Italy on 23 November 1980, leaving at least 2,500 people dead, 8,000 injured and 250,000 homeless, the town in the heart of the Sannio area was evacuated and its residents moved into what has become the new Apice. Only recently the narrow streets and the tragically abandoned buildings have started, slowly, to repopulate. (Photo by Cesare Abbate/EPA)

A woman is cooled down with a watering can as she sunbathes using insulating tape, at a beauty center in Belo Horizonte, Brazil, on December 21, 2017. Brazilian women take advantage of the beginning of the summer to sunbathe using the new national trend: natural tanning with insulating tape. Instead of using tiny bikinis on the beach, women avoid being bothered or stalked by getting taped in the shape of them, and lay in the sun over rooftops to enjoy the morning sun and get the perfect “marquinha” tan lines. (Photo by Douglas Magno/AFP Photo)

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.

Kha Tu Ngoc rests in her two- square- meter house in Ho Chi Minh City on May 2, 2018. The “micro- house” dwellings are dotted throughout Vietnam' s bustling southern hub, occupied by families clinging to postage stamp- sized plots a city developing at breakneck pace. Tucked away in winding alleys, nestled under new condo developments or sandwiched between street food stalls and shops, the tiny houses are easily missed by the unattentive passerby. (Photo by Thanh Nguyen/AFP Photo)