Your weapon controls allow up to 8 buttons. This is quite a lot, but sometimes you want to accomplish things through specific combinations of buttons - without getting trapped in a maze of A_(Clear)Refire hacks trying to trace a unique path for every possibility.
- Dual-wield (or double-barreled, double-triggered) weapons: each of the two fire buttons handles one weapon, and each weapon (which is on a different overlay from the other, of course) can be fired totally independently of what the other is doing - even if the other fire button is still being held down.
- Heavy Weapon Guy-style gun spinup: hold altfire to keep your gun ready to fire at any time.
- Slam fire shotgun: hold trigger down, hold altfire to rack the shotgun, gun immediately goes off once you chamber the new round.
- Panic shot: shoot in the middle of a reload sequence, spending whatever happens to be in the chamber already.
- Check for holding Zoom/Reload/other non-A_Refire-able inputs outside of a ready state.
- Daggerfall-style melee weapons: hold button, move mouse in the direction to swing.
- Wacky weapon with a "jamming typewriter" interface that prevents the weapon from operating if you mash the buttons too fast.
- Spellcasting decision trees.
- Crude musical instruments.
- You have actually run out of buttons for calling all the various weapon functions you have coded.
EDIT: Example of how this looks in application: