Talking to a playwright friend of mine, she put forth the following:
"A plot twist takes the story in a new direction, while a reveal answers a question."
Applying this to RPGs: Plot twists make good act breaks and raise the stakes. Plot twists can go at the end of sessions. However, since they change the direction the drama moves in, they really don't fit into 4-6 hour sessions.
Additionally, a reveal can be a plot twist - new information can raise new questions.
Complicating things further, a plot twist can not be a reveal. Taking the story away from the original conflicts can't, in itself, answer questions.