The temperaments are often described in terms of energy-- Extraverts having a higher amount of energy, and Introverts having a lower; J-types having a more steady stream of energy throughout the day, and P-types fluctuating.
Physics teaches us that energy cannot be created or destroyed, only transferred and/or converted into other forms.
So, how might this law of physics affect a given group of people?
A room full of Extroverts (no Introverts)-- The high levels of energy are continually being passed around, bouncing off the walls, transferred from one person to the other, etc, resulting in non-stop energy and excitement.
A room full of Introverts (no Extroverts)-- Energy level is very subdued. There is no Extroverted energy around to prod anybody into action, so everyone is probably just sitting around, doing his or her own thing, mostly in his or her head. There may be some conversation, but nothing really animated.
A good social gathering (or work environment, or whatever), then, really requires a fairly even distribution between Extraversion and Introversion. Some of the Extraverts' energy will be transferred to the Introverts, helping the Introverts gear up, while also helping the Extroverts to become more calm and focused.