One example is how "educated" speech is used as a means of gaining power. There is power in the ability to appear to have a large vocabulary; using speech eloquently adds credibility to a speaker and can completely transform the way a speaker is perceived.
For example, taking a look at prominent recent political figures, say, presidents such as Bill Clinton and Barack Obama, it would be difficult to argue that their persuasive power would be as high without their ability to speak well. They have used their skill in articulation to appeal to people on all levels and classes and have become figures known and respected for the command of language and speaking ability they possess.
But language can also be used in this way to manipulate. Often, less educated peoples may have greater respect for someone who uses "educated" or "higher level" language simple because of what they feel it represents. This can be dangerous if the person or entity does not deserve respect otherwise and uses that command of language in a negative way. Language in a political speech, contract, or disclaimer may seem "educated" and therefore "credible," even when it may be extremely obscure.
This shows why the political power of language is important. It can be used in an array of ways, positive or negative. And to deny its power is to deny the accomplishments achieved and injustices committed with it.
