From a theoretical stand-point, death pits seem to have no obvious advantage to me. Once learned, they're easily avoided. Until then, frustration. As a rule of thumb in multiplayer, the level should be a tool the player uses to beat the other player. The player should never have to wrestle with the level to use it. In single player, it's obviously player v. the level, though, so they're more appropriate there. Given that as a player learns the level, they'll eventually avoid pits entirely, they become pointless features. Maybe you can score something from pushing somebody into a pit. But does that really justify their usage?

Oh, and if I had heard about the pit feature before this, I would have pretty much said the same thing =|