The M7 SMG is always a devastating weapon when dual-wielded against Elites and Brutes, and is brutal against Grunts and Jackals and Flood forms. It is, however, less effective against Drones, as their erratic flight patterns make them hard to target.
Dual-wielding an M7 SMG with a plasma-based weaponry works extremely well against against shielded targets.
Short, controlled bursts with a single SMG is required to maintain ammo and effective range when engaging Covenant forces.
In Halo 2, the M7 is not a sound weapon to start with, but if no other option is available, minimize being killed by staying in a safe zone until a better weapon becomes available.
If stuck with an M7, stay in close quarters, and do not venture out where an opponent can take the player down with longer-ranged weapons.
Dual-wielding the M7 SMG with a plasma-based weapon such as the plasma rifle works very effectively against shielded targets. Dual-wielding an M7 and a pistol can be tactically useful, as it can create a deadly combo that can take out targets quick and efficiently. However, it requires a great deal of skill and hand-eye coordination. The combination of a full-auto and a semi-auto weapon can be confusing and hard to handle when aiming at an opponent.
The M7 is a good choice as a suppression weapon, because of the sheer volume of fire being produced if dual-wielded, especially when engaging a nearby BR55HB battle rifle or sniper rifle.