Aspects of style can represent the overt intent of the speaker to influence in a particular way or establish a particular emotional tone. Trying to be informative, persuasive, or entertaining can represent the purpose or role of the speaker - there is nothing inherent in discourse that necessarily establishes this speaker intent. The description of an automobile accident may be informative to some, persuasive to others, and even entertaining to a few regardless of the speaker intent. On the other hand, if the intent or role of the speaker is developed in terms of audience analysis it has a better chance to carry through to listener responses. The appraisals people make as to style can on the one hand contribute to the success of the communication or it can tend to shut off communication.
Style can make a person well worth listening too or it can make a person seem stupid and bungling.
If a person wants to sound knowledgeable, competent, educated, and polished then that person will develop correct language vocabulary, correct grammar and sentence structure, and specific word choice. The person will strive for proper physical support to complement the language used. The person will tend to sense what stimulates certain responses in the audience and then both consciously and subconsciously make choices that could achieve the desired image goals he has set for himself. He may analyze his audience in terms of age, sex, ethnic background, economic status, educational levels, etc. in order to achieve that self perceived style he wants the audience to award him. Hopefully, the style awarded you by your audience will complement your role, purpose, and intent as a speaker.