As with most corporations, my company's conference rooms include large tables ringed with chairs, and a few scattered chairs backed against the walls. I am always dumbfounded when someone comes into the room and sits in those wallflower chairs. Even when the table seems full, there is always room to squeeze one more person in.
People seem to sit on the edge for two reasons. Often they perceive the table to be too crowded already. They don't consider themselves important enough to crowd in. Which brings us to the second reason, the don't consider themselves worthy to sit at the table. They defer to the people they see as more important than they are.
Neither of these is a good reason to be a wallflower. When someone sits on the edge of the room, rather than at the table, they prove to everyone that they don't belong at the table. The edge is neither a leadership position nor a follower position. It is a position of inaction.
The only time I recommend sitting on the edge is when leaders need to push their teams to run more effectively without their constant input. Even then it is usually better to not attend the meeting at all.
No matter how low your stature, or how senior the meeting, you need to sit at the table unless you are asked not to. Be presumptive. Push right up with the certainty that you belong there. You can't be a real participant from the sidelines. And, you can't expect to be successful if you don't participate.