This is the worst level in the game, not in terms of quality but in terms of dickishness, and for that reason, it is one of the best picks. There is only one reason to pick this level, and it's because you want to be an absolute jerk. There is NOTHING of value in this level - it has fewer enemies than any other level in the game, it's a total timesink, there is no reason to go here. It is just a barren, hellish landscape - and probably the most difficult level to survive when you have a lot of coins. You can tank Lakitus and Hammer Bros and Bowser but you can't tank falling into a pit, and this is probably the most acrobatic level in the game. If someone gets to this level, there is a damn good chance they will die. You won't get a KO off of it, probably, but you will laugh at their misfortune, and this level out of any level probably has the highest chance of picking off experienced players without just waiting them out, so I think there might be reason to pick this. Of course, you also have to survive it, but that's fun, right?
for the record, this was the level that took me the most attempts to clear unlockways just because it is such BS. =O