traps can be VERY useful for softening up tough enemies. The best situations for setting up traps are the occasions where you are POSSIBLY going to fight something that is not your enemy yet. For example, in the very first dungeon there is a room with 2 golems just standing there. Neither one is hostile to you so you are allowed to set traps at that time (you cannot set them with enemies around). After you set the traps, THEN you force an attack on a golem, causing the golem to go hostile which then triggers the traps, damaging it greatly. You can use this tactic in all sorts of situation for some fairly nasty enemies. Some that I have used this for are Golems, Dragons, the room upstairs in the Den of the Seven Vales (Waukeen's Promenade), some Liches, etc.
Just use the traps in situations where you know you will end up fighting but are not hostile yet, that is the main point I am trying to get to...
Famous Last Words in BG2:
"I didn't know they could do that?!?!?"
*load last saved game*