"A man with nothing to die for has even less for which to live." -Guerrand DiThon
Dragonlance is a shared universe created by Laura and Tracy Hickman, and expanded by Tracy Hickman and Margaret Weis under the direction of TSR, Inc. The authors took an active stance against racist ideology and clearly assigned races as "good" or "evil"; emphasizing the need for tolerance and cooperation between the races. Dragonlance is one of the most popular D&D settings of all time, just behind the Forgotten Realms in terms of popularity.
Dragonlance is set on the world of Krynn, usually in the various regions of Ansalon, a small continent, though some have taken place on the continent of Taladas, located northeast of Ansalon. Depending on the time period, the evil chromatic and the good metallic dragons are rare or plentiful. Humans are Krynn's most common humanoid race, but elves, dwarves, kender, gnomes, and minotaurs occupy the world as well. Draconians are created by corrupting a dragon egg and used for armies.
Dragonlances are weapons designed to kill evil dragons, and are the only weapons with which mortals who cannot use magic can kill dragons. Dragonlances are rare and not commonly traded. There are lesser dragonlances, which are made when only one of the artifacts is used to create them, and greater dragonlances, which are made when both artifacts are used to make them. Greater dragonlances are blessed with the power of Good, unlike lesser dragonlances. There are two sizes of dragonlance. The smaller footman's dragonlance is around eight feet long and functions as a pole weapon, while the larger mounted dragonlance is around sixteen feet long and most commonly used when mounted on a dragon.
No self-respecting dragon would let just anyone ride them. If somebody is riding a dragon, be afraid of the rider not his mount.
The benefit of dragon-riding for humans is obvious - a fire-breathing mount of immense power, a beast able to carry the largest Dragonlance into battle, and a highly intelligent creature as an ally. For dragons, the rider posses the means of wielding the Dragonlance they carry, especially helpful against other dragons on the battlefield. The rider can write down information, relay information back to the ground, and help the dragon identify the correct target - most humans will look identical to them. Dragons are powerful, but other dragons, ballistae, cannons, and magic from large scale battles can seriously wound them. A rider acts as an extra set of eyes and someone that can administer aid or defend them should the worst happen. A mage rider can shield against attacks and prevent mind-control spells.