I actually didn't realize how often they're used until just now haha.  I don't have a definitive answer, but I'd imagine one reason is that it makes writing or reading long terms that are used often more efficient.  For example, in history class just writing/reading "WWII" instead of "World War II."

Also, it can be used as a way to condense a certain method or set of rules.  One I learned many times is for the proper way to set goals, referred to as SMART goals which stands for Specific, Measurable, Attainable, Relevant, and Time-bound.  By using the SMART acronym, it makes remembering these set of rules easier and also takes less time to read or write.

Bill, I appreciate your correction (I wrote "I trying" seriously? hahaha What a stupid) I agree with your statements, specially number 4. Besides, your observation about communication slowing down is very enlightening.
Evan, Efficiency! IMO this is the word that encloses the whole meaning of American culture and this is evident in every context, life, business, politics and so on. After all the efficiency principle is at the basis of Taylorism as well as Fordism.
Sara, nowadays acronyms are used everywhere but IMO for American culture is more than a way of shorten words is just about an institution. The incredible thing is that Americans were able to transform acronyms in real words that are used in a daily basis. Laser, radar ect. 

I AM trying to understand if this is a part of their culture. I mean I want to know if for Americans IT is a way of speedING up processes in every context.

1) it confirms that the person is "in my culture" so a secret password :-)

2) it excludes people who do not know the meaning and allows those who know the FLA (four letter acronym) to be superior to those who do not

3) it speeds up data transfer but slows down communication (this is a subtle difference but often noticed by European English speakers when working with American English speakers)

4) it helps develop "group-think" which in a nation of individuals is important

5) it saves on type face and typing time