This has some odd effects:
If you shoot into a dark area, but there is no one to hit, the game won't let you shoot. On the other hand, if there is a target, you will shoot. If you miss, there is no way for the player to distinguish between these actions.
(if you hit, you get the floating damage text)
If something out of sight casts a spell at you, you don't get a sound effect. For me, since I play with sound on, that makes me think it's trap damage (since traps have no sound). So I just sit there and wait for it.. With npcs like fire imps (that can cast every round), the trap illusion is reinforced by damage each round. It would be nice to get the sound effect to tell me that I'm under attack from a spellcaster
(even better: if the npc that just cast a spell at me were revealed, like with Track)