I have tried to get similar bunker philosphy threads going here, but they often fizzle, but its a great question. Bunker theory.
While some here always answer "it depends on the land" (and of course, ultimately it does) I think having a strong idea of what you should do with bunkers is good. I always say that bunkers are 4x harder for the handicap player than the scratch. I think the idea of variety is a good one.
Some old and new bunker theories I generally adhere to:
My tendency is to make fw bunkers on par 5 hole LZ areas deeper than most, feeling you might cost birdie, but you won't cost par.
Ross and others tended to make par 3 bunkers a bit deeper because you are hitting from a tee.
Dick Nugent always favored a "master bunker" (i.e deeper) that set up the hole, but realizing the aesthetics of bunkers, often added several that were shallower, as much for looks as anything. The key is to know which is which from the tee!
I (and others) also relate bunker depth to distance, with greenside bunkers generally deeper than fw bunkers, because you are hitting a wedge out. When the land allows, I try to make bunkers on long par 4 shallower than shorter par 4's, to accomodate the expected long iron shot to recover.
Sometimes I adjust depth for a particular situation where they are very likely to be hit, such as a narrow green on a crosswind hole. Or, I substitute a grass bunker in place, especially in places like short right of the green.
Would love to hear contrarian views......