And one particular point to add is that if the flight crew - usually the First Officer - needs to visit this area just before planned take-off, then it may well be a cabin full of passengers, maybe wearing coats and hats, some asleep. By having the triangles the crew can go quickly to the right spot and disturb just a few people briefly to the see the wings, rather than alarming a larger group of passengers for a longer period, trying to find the right spot.