Console would be very useful if you want to read messages you were unable to read because they disappeared fast, or to configure the game using more options than the ones offered in options menu, display your game version, or even to warp to a map.
However some people are having troubles figuring out how to open it, here's a quick step-by-step guide on how to do it:
- Open your DOOM 3 Folder and double click your "base" or mod folder
- Open autoexec.cfg using notepad, or create it if it wasn't there
- Add the next line to it (without replacing any of the existing lines) : set com_allowconsole 1
- Save and close
- Open the game and press CTRL, ALT and ~ keys together (in some countries you will have to press CTRL, ALT and the key directly beneath the ESC key if ~ doesn't work)
Tip: type "unbind ctrl" if you don't want the game to fire your equipped weapon every time you open up the console (unless you use CTRL for firing)