Running It Twice (or More)

[East Bay Rounder]

In a cash game situation, why would someone ahead in a hand want to "run it twice"? To my knowledge, when this happens, the pot is split in two, so the winner of each "run" wins half the pot.

The way I see it, if you are a proponent of this, you'd lose money in the long run, plus you give the underdog an extra chance to win a pot he's behind in, without extra financial compensation.

Thoughts?