This buff is applied to increase the defensive capabilities of the units around the commander. The buff also gives a slight reload speed increase and movement speed decrease.
Soldier is a very weak form of infantry, usually dying faster than other classes. However, the high amount of bullets and low recoil of the Automatic Rifle means that you can generally 'spray and pray' the weapon. However, it is best to always aim for the head for much higher damage.
An agile soldier can cause problems to snipers in close range, able to dish enough damage for the snipers to run back, and in some rare cases, manage to kill them. This will not be the case for Havoc and Sakura since they have a more damaging automatic Carbine.
The lack of cost of the Soldier also makes it a nice scout in the field, it is versatile enough to fight back any opponents long enough to give intelligence of the enemy faction's current tactics/positions.
Soldier is weak with a weak weapon. You can kill him with generally any weapon you have. They should not be ignored, but they're on low priority unless they're carrying beacon/airstrike, close to the Master Control Terminal or are about to plant Timed C4 on vehicle.