When does it pay to play deep?

Originally Posted by Fnord

At least one of 4 things must be true:

• Your opponent will call off his entire effective stack with too wide of a range of hands.
  You opponent will bluff off his entire effective stack too often.
  You can read your opponent's hand well enough to get in an extra value bet or value bluff if you played an additional bet/street.
  Your opponent will fold medium strength hands to implied threat on what otherwise would be an all-in street.

I'll argue that if none of these are true, you're better off with less than 100x the Big Blind. Although I'm not sure about the last one. Any others I might have missed?

One of the reasons i dont play deep anymore in med stakes games is because all decisions 100bbs deep are 'standard' with enough hands played for experience.
One reason i would play much deeper is if a player is not just bad for above reasons but if they are incapable of second+ levels of thought in medium-large pots, which probably indicates point 4 you make.