A friend of mine does this in e-mail. I've just asked her, and she says it's because with more dots she wants the reader to think longer. As in:

"She disappeared with John for two hours the night of the party... Not that I'm going to ask her what happened, you know..."

is different from:

"She disappeared with John for two hours the night of the party............... Not that I'm going to ask her what happened, you know................."

Can you see any difference?