No inspection-ready unit has ever passed combat. Teamwork is essential. It gives the enemy other people to shoot at. If the enemy is in range, so are you. Friendly fire isn't.
Tracers work both ways.
The only thing more accurate than incoming enemy fire is incoming friendly fire. Radios will fail as soon as you need something desperately. Professionals are predictable, but the world is full of amateurs. All-weather close support doesn't work in bad weather. The bursting radius of a grenade is always one foot greater than your jumping range.