Language and style

It becomes more formal, much more concise, and the kind of diction used changes significantly. You attempt to show a more mature and intelligent side of yourself than you would feel the need to with friends. If you were too formal and impersonal when talking with friends, they might think you're not really friends, or that you don't feel connected to them. With family, its even more so informal and colloquial, and you are able to hopefully show all of your own personality when talking with them. However, it is necessary to show a little restraint rather than with your friends, as they are likely to disapprove or become indignant at your communication, because they likely perceive you as a good person still.