I prefer to use it on a drivable par-4 or short par-5, where it punishes the player who shouldn’t have gone for the green. On a short par-3 it’s just window dressing, and on a 400-yard par-4 it is a slap in the face to greens fee payers.
Then how do you justify the bunker 40ish yards short of the green on the 440 yard 4th at Bel Air? Unlike the bunker 40 yards short of the green on the long 5th at Merion, which protects against a weak shot bouncing onto the green, the bunker at Bel Air primarily punishes the weak golfer who probably can’t reach the green in regulation.
If the answer is because that’s where it was 100 years ago, that’s not really much of an answer. 100 years ago, good players were hitting long irons or fairway woods into the green.