When referring to combat (as opposed to firefighting), a fire team is a subset of an infantry squad, which is a subset of an infantry platoon. There are usually four squads in a platoon, with two fire teams per squad. This enables the platoon to better organize its firepower to address different threat levels and patrol issues. A fireteam is also the smallest military unit that still contains a mix of weapon types.

The benefit of a mixed-weapons combat unit cannot be underestimated. A machine gun has a high rate of fire, but needs support from riflemen who can accurately engage the enemy at range and who can move without the weight penalty imposed by the heavier weapon. They in turn benefit from the indirect pseudo-artillery-style support a grenade launcher provides.

The usual weapons mix for a US Army fire team (with some variations involving different weapons that may be mission-specific) is:

One M249 squad automatic weapon
One M203 grenade launcher/rifle
Two M16A2 rifles