Communication can be interpreted in different ways by different audiences. With a small group you may not have to put as much emphasis and attention on the point you are trying to get across as you would with a large group. If I were to communicate a message to a small group as my board I would do it with a small informal meeting, where I would present the importances of the message along with supporting questions taken from the group.
If I were to present the same message to a larger group, a entire organization I would have to set up a conference or a mandatory organization wide meeting to portray the message I was trying to effectively get across. This type of meeting would not allow for questions and discussions, due to the amount in attendance, as where the Board meeting would. There are effective ways to get your message and point across also, for instance presentations, and company wide memos.
In order to decide which communication method is or would be more effective you have to decide on the type, amount and nature of the audience and message you are trying to get across. Effective communication is important in everyday functions as well as leadership and business. In order to properly convey yourself, your ideas, and your values. In order to be a effective leader you must posses the necessary communication methods to ensure that you are taken seriously and with doubt, especially in the high paced business world we are in.