You shouldn't chat about non-business-related things during a business meeting.
Tom sees his friend and colleague, William, at a weekly sales meeting and decides to sit next to him.
Tom wants to find out what William will be doing during the upcoming weekend.
Tom takes care of business at the meeting and waits until after it is adjourned to talk with his friend about social issues.
Tom ignores the meeting agenda, and the other participants, and starts talking with his friend about possibly having a bar-b-que over the weekend.
The meeting is productive and Tom is able to plan a nice weekend event with his friend, without sacrificing his work ethic.
The other meeting participants become visibly annoyed with the chatter and Tom is embarrassed.