The tee shot on the 16th is defined by out-of-bounds along the right side, and the Principal's Nose bunker complex, with the Deacons Sime bunker beyond it. The question of whether to lay up or try to play long and try to stay in bounds.
The approach from the lay up position is challenging, likely a long iron, with Grant's bunker and Wig guarding the safer, left side of the fairway.
Aggressive play will lead to one of two results, either a comfortable wedge into the green, or a sand wedge out of one of the deep bunkers.
"The bunker in the middle of the fairway is an especially controversial topic... The par-4 16th hole at St. Andrews, defended by a cluster of fairway bunkers known as the Principal's Nose, is the classic example... The weakest players do not worry because they will not reach the central hazard with their drives; others will aim straight at it, confident that their usual inaccuracy will prevent them from harm. For the accomplished golfer, the key to the hole is the green, oriented so that the approach is much easier from the right, where the hole is bordered by out-of-bounds. Some of the better players play short of the bunker for safety, and are content to play a longer club for their approach shot. Others may try to use their power to drive over the hazard, while some will coll on their accuracy to slip by the bunker. In other words, every player has the chance to avoid the hazard in his own way."
-- Tom Doak
"Twenty years ago I described the 16th at St. Andrews...
'As in the majority of good holes, it is the subtlety of the slopes that makes it so. The green is tilted up slightly from right to left... the approach from the right is easy, as all the slopes assist the players, and the approach from the left is exceedingly difficult. The point about the hole is that it is so difficult to get into the best position to approach the green because of the proximity of the Principal's Nose bunker to the railway... there is a perfectly easy route free from all risk to the left... but the player in all probability will lose a stroke by taking it.'
This description of the 16th was entirely wrong...
Ted Blackwell is a man of action, but few words... I watched him play the hole... and noticed that when he placed his drive [10 yards left of the Deacon Sime bunker], he played a run up approach so near the flag that he not infrequently got a three. I then discovered that he took advantage of a small valley (which I had previously overlooked) in the bank of the green leading up to the place where the hole is usually cut on medal days.
If the tee shot is placed ten yards to the left... or right, the advantage of this valley is lost.
Is there any course in the world that presents such subtle strategic problems?"