Why are hormones used anyways??

The way that implants work are rather simple. The growth promotants work by changing what happens to the nutrients that animals eat into muscle rather than fat. Muscle grows faster than fat so when the animal can grow more muscle than fat, this reduces the time it takes to reach the goal weight of the animal. 

Meat on the left is very lean and meat on the
right is overly fatty 
 

Since cattle are able to produce muscle faster this also increases the leanness of meat. With lean beef, you get the nutritional benefits while avoiding much of the saturated fat known to increase the risk for heart disease.

The FDA website states “Since the 1950s, the Food and Drug Administration (FDA) has approved a number of steroid hormone drugs for use in beef cattle and sheep, including natural estrogen, progesterone, testosterone, and their synthetic versions. These drugs increase the animals’ growth rate and the efficiency by which they convert the feed they eat into meat.”  It is very surprising to many consumers when they find out this fact from the FDA. They are often unaware that implants are not a new practice in the beef industry.

By taking less time and less product farmers are able to cut out costs in production. According to the article Growth Promotant Use in Cattle Production, Growth Promotants improve cattle growth rates and feed conservation efficiency, increasing annual U.S. beef production by more than 700 million pounds while saving more than 6 billion pounds of feed. Personally, I think that is a huge number to think about.  

 Sources:
 http://www.fda.gov/AnimalVeterinary/SafetyHealth/ProductSafetyInformation/ucm055436.htm
 http://www.explorebeef.org/cmdocs/explorebeef/factsheet_growthpromotantuse.pdf