**SPOILER**
I tried extinguishing all of the torches in Act I-Citadel Level 3 because the "writings on the wall" seemed to hint "in darkness you will see," or some such. However, the only success I had was in Area #6 (see map in the link below). In the side corridor to the left of the main corridor, if you extinguish the torch in this side corridor, then an exit opens up at the other end. By using this side corridor, you avoid all of the traps that are in the main corridor.
http://beyond.divinedivinity.net/help/citadel03.jpgIn Act I-Citadel Level 2, you unlock the door to Area #4 (see map in the link below) by extinguishing the torch next to the door.
http://beyond.divinedivinity.net/help/citadel02.jpg