Somebody recently brought up the question of how I decide the amount of people I let into my group. This is an interesting question because I think size is an issue too frequently overlooked, especially amongst teenage DMs. All too often when starting a new game you mention it causually to a couple people..then on the day of the event ten PCs show up at the door causing a mini heart attack.
My group at the moment contains 7 PCs, a very large amont for a group. The original number wad an unheard of 8 players. There are certainly a large lists of pros and cons associated with different group sizes.
I decided to let so many people into the group simply because there was a large group interested. My goal was to expose as many girls to dnd as possible. And the experience has been rewarding. It allowed the group a chance to bond, giving them a common connection to talk about in their everyday lives. Having a big group also allows a lot of diversity to come to the table. Great players can mix with the not so great, there is a wide array of pc personalities, and many different story access points for me to use. Similarly it makes the social aspect of dnd very rewarding because it's a big group gathering.
On the flip side large groups can be very difficult to manage. I personally combat this issue by drawing on my experience as a director combined with Machiavellian principles outlined in "The Prince." large groups aremoreprone to disruptive bouts ofconversation and joking that keeps anything from getting done. Keeping sessions regular is also more of an issue. Trying to scedule a day that works for 7 people is significantly more difficult then doing it for 3 or 4. We combat this issue by establishing a quorum rule. The "rule of five" states that we can play if at least 5 PCs are present.
Two days ago I DMed my smallest group ever. Two of my PCs had their own adventure within the adventure. There are definite benefits to groups this size. The game flows more quickly, is easier to control, and easy to scedule. My favorite thing about small groups however, is how truly personal the game can get. DMs can more easily make plot lines that tie directly to PC backstories, making the game all that more interesting. It becomes a pleasure to create situations that cause PCs to question their characters morals and motives. And their is no better feeling then making your pc so attached to their character that they physically tear up or gasp in horror.
In any case, most people have a perfect number that works for them. Every individual though has the ability to make a game perfect for the party size.