Map Creation
A team color can be chosen during the map creation process, among six different options. This is mainly for a frame of reference during the map making process. If a player prefers a certain armor color during a run-through of a map, he can choose that. Armor color permutations also may be a factor in certain maps, allowing players to blend into or stand out of certain environments. These discoveries can then be saved as map options, with the teams choosing between the two best armor colors as determined during map creation.
Game Play
Gametype variations include capture the flag, slayer, king of the hill, or other objective or slayer variations. After you have made and saved the map, two or more teams compete for "kills," flag captures, or control of territories on the map. Without the ability to make teams in "Forge," these gametypes would be impossible -- since they are team games -- thus rendering "Forge" an interesting diversion with little use.
Practice
In "Forge," teams can divide up into core red and blue multiplayer scrimmage squads, practicing moves and expected strategies employed by other teams. The ability to have complete control over any map, weapon layout and vehicle presence works in conjunction with the ability to choose the two colors used in traditional "Halo" multiplayer. For dedicated competitive teams, these abilities allow them to explore and take into account any contingency.
Saved Films
A unique feature of "Halo 3" and "Forge" is the ability to save custom files and upload them to Bungie's servers for all to view. Many times, "Halo" enthusiasts will make machinima, or animation using video game assets. Rooster Teeth is a well-known group that is famous in the "Halo" community for doing this at a high level, via their "Red vs Blue" series. The ability to choose any team color in "Forge" allows character differentiation and variety in these machinima file episodes.