- Especially in the early stages, a relationship is being built and trust is being established. Having excess people in the room can distract from that goal.
- You want all parties to leave meetings feeling as though something significant has been accomplished -- the ball has been moved downfield. Having too many people with too many different agendas, lines of questioning, approaches to the problem, etc., can clog the conversation and prevent that from happening.
- The simple fact that one side brought many more people to the meeting than the other can become the most memorable aspect of a meeting, distracting from the point.
- Too many people in the room, especially on the side of those seeking funding, can come across as weak. Why did so many people come? Is there a lack of trust? A lack of shared belief in other peoples' abilities? Is somebody afraid they're going to be left out? Is somebody desperate?
While I have seen the above happen on several occasions, there can be exceptions. In situations where there are multiple kinds of expertise involved you may need several in the room. Or you may want to create a feeling of superiority over the other side to drive home a point. In those case, definitely bring all the people you need. Otherwise, limit the number of participants to just the people needed to build and improve the relationship.