If you are giving a pep talk to five classmates in a very small room, the situation demands an informal speech. It is not likely that you would prepare for days, nor is it likely that you would carefully practice the speech for hours before you deliver it. If, however, you are asked to speak to an audience of five hundred in an auditorium, you will want to prepare your speech carefully and formally. In general, the larger the audience, the more prepared you should be. Indeed, the larger the audience, the more you must rein in informality, slang, and inside jokes. Of course, there are situations in which a small audience requires a lot of preparation (for example, a sales pitch in a boardroom). But in general, the bigger the audience, the more you should prepare.