My idea of having bunkers on a particular hole is to make the golfer think about his tee shot or maybe a approach shot into a green. It should have some type of strategy involved.
I have always been of the opinion that fairway bunkers should be like a light-house. It could be an aiming point to hit at or maneuver around. The closer the golfer can get to the fairway bunker the more reward he should get i.e. an easier approach.
However there are times when fairway traps should be impossible to get out of these should only be used when you want the golfer not to hit the ball in this direction as there are either houses, road's, or just people walking past.
I also believe that the lip on fairway traps should give the golfer a chance to hit the ball onto the green and not just be a straight out sideways with a sand iron.
Green side Bunkers
I am of the opinion that a bunker should not be in front of an opening to a green. The only time this should happen is when the golfer is faced with a short iron to the green. As you can see with the green to the left that it has a wide opening, and plenty of room to run the ball into the green. The bunkers should be set to the sides of the greens to collect the wayward approach shot. I must say that the amateur is more affected by the thought of going into the sand.
The hole below is a great example of how a traditional greenside bunker is designed. There is a large lip on the front. The layered grass seen in the face gives it caricature. Also notice the low walk in area between the traps to help the golfer walk into & out of the sand. All to often the re-designed and new golf courses do not pay enough attention to this aspect.