In addition to Trev's informative reply I'll say that hotseat is also handy for not - much competitive game style - like myself playing ocasionally civ with my wife. It is a variant to consider if you have no network of any type or stuck with only one pc in one room. Back in the days it was the common multiplayer game type. Super artillery, Warlords, Khan2, Heroes of Might and Magic 3 comes to my mind.
Pitbosses are long- time investment. They last for about 1/2 to 1 and 1/2 year depending of the settings. You get to know the people you play with better, even if you don't know them in the real life, you build up reputation, think a lot when making decisions, and a lot of diplomacy is needed to be made.