Question: Why are some sleds faired?
About the article "Scuba diving", section "Diver propulsion".

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Personal mobility is enhanced by fins and optionally diver propulsion vehicles.
Fins have a large blade area and use the more powerful leg muscles, so are much more efficient for propulsion and manoeuvring thrust than arm and hand movements, but require skill to provide fine control.
Streamlining dive gear will reduce drag and improve mobility.
Balanced trim which allows the diver to align in any desired direction also improves streamlining by presenting the smallest section area to the direction of movement and allows propulsion thrust to be used more efficiently.
Occasionally a diver may be towed using a "sled", an unpowered device towed behind a surface vessel which conserves the diver's energy and allows more distance to be covered for a given air consumption and bottom time.
The depth is usually controlled by the diver by using diving planes or by tilting the whole sled.
Some sleds are faired to reduce drag on the diver.
Extreme sledding is a sport where riders do not simply sled down a hill, but use the sleds and their bodies to carry out various tricks, using apparatus such as ramps, rails, ledges, and some that are performed simply riding down the hill.
The types of tricks that are carried out borrow certain characteristics from snowboarding, skateboarding, aggressive in-lining, BMXing, and motocross.
Extreme Sledding can use many different types of equipment, with the most common being "knee-sleds" which are sleds where you ride on your knees, (sometimes strapped on). 
Samuel Leeds Allen patented the flexible flyer in 1889. in Cinnaminson, New Jersey using local children and adults to test prototypes.
Allen's company flourished by selling these speedy and yet controllable sleds at a time when others were still producing toboggans and "gooseneck" sleds.
Allen began producing sleds in his farm equipment factory to keep his workers busy even when it was not the farm season.
He developed many prototypes before he created the flexible flyer.
The sleds did not sell well until he began marketing them to the toy departments of department stores.
In 1915, around 120,000 flexible fliers were sold, and almost 2,000 flexible flyers were sold in one day.
In 1968, Leisure Group of Los Angeles, California bought the S. L. Allen Company.
Leisure Group continued to produce flexible flyers in Medina, Ohio.
In 1973, a group of private investors bought Leisure Group's toy division and started manufacturing the sleds under the name "Blazon Flexible Flyer" in West Point, Mississippi.
In 1993, Roadmaster purchased the rights to production and moved production to Olney, Illinois, and in 1998, production was moved to China.
As of 2012, Flexible Flyers are mostly made in China and some are made in South Paris, Maine by Paricon, Inc. 
s for competitive sledding.
A few types of sleds are used only for a specific sport:  Bobsled (British bobsleigh), an aerodynamic composite bodied vehicle on lightweight runners  Luge and the skeleton, tiny one or two-person sleds with runners Various types of sleds are pulled by animals such as reindeer, horses, mules, oxen, or dogs. 
The people of Ancient Egypt are thought to have used sledges extensively in the construction their public works, in particular for the transportation of heavy obelisks.
Sleds and sledges were found in the Oseberg "Viking" ship excavation.
Sledges were useful not only in winter but can be drawn over wet fields, muddy roads, and even hard ground, if one helps them along by greasing the blades with oil or alternatively wetting them with water; in cold weather the water will freeze to ice and they glide along more smoothly with less effort to pull them.
The sledge was also highly prized, because – unlike wheeled vehicles – it was exempt from tolls.
Man-hauled sledges were the traditional means of transport on British exploring expeditions to the Arctic and Antarctic regions in the 19th and early 20th centuries.
Dog sleds were used by most others, such as Roald Amundsen.
Today some people use kites to tow exploration sleds in such climes.