The result can be that nothing gets done. Humor is a great stress reliever, but it should not be a substitute for action. When you see it interfering with the meeting, you can always take the person aside and discuss the issue. Also effective is failure to respond to the humor. At the heart of a meeting is the agenda.
Several suggestions are worth emphasizing.
The agenda should match the time allotted to it. If you have a half-hour to meet, put in only half an hour's worth of material. A good tactic is to provide a time limit for agenda items like that shown on p. 464. I have found that when time for an item runs out, people are generally ready and willing to vote on the issue. Without this, debate can go on and on especially from dominant members who waste time to slow action.