When is it time to unleash the Big Gun?

Question

The BFG 9000 is a big gun that fires giant balls of green plasma, which usually destroys everything in the general direction that you're pointing the weapon when it discharges. It has a warm up time, a charging time, and a firing time.

In DOOM 3, you take damage from being too close when the weapon discharges, and the weapon can be 'charged' to the point where the gun explodes, killing you instantly.

Because of this, this guns' use is somewhat situational, you can't charge it too pre-emptively else you will die. You can't discharge it in a narrow space else you will die. You can't discharge it with an enemy in front of you or... you get the idea.

When is the best time to use this weapon instead of another gun?

Which enemies need more than one or two levels of charge from this weapon in order to die?

Answer 1

Most players get used to the tempo of the gun, so overcharging isn't an issue.

Most players move backward while charging so hitting the wall at end of the tunnel as in your screenshot won't get you hurt.

It shares many characteristics to rocket launcher so they have very similar tactics. You can inflict damage with indirect hit. It may not kill the enemies but from indirect hit it saves lot of ammo for other guns. Most boss moves slow so it is not difficult to have direct hit on them even at long range. My preference is to use it at medium to long range, which the enemies are trapped or behind the wall.

You may score lucky hit in multi-player at medium range, as everyone keeps moving and jumping. It is also suitable for suicide attack at close range, although it is kind of difficult to get a BFG in multi-player game and the charge up time would becomes an issue. The psychological effects at close range is also great to novice player too. You may also scare them to have mistake while jumping on difficult terrain.

You can have more information from here.