Only use of dream manipulation I've found so far is Fawn. If you're living together, sometimes she'll be asleep when you come home. You can use it on her then.
Since I asked this question, I've managed to find another place: a private room in the Tower of the Succubus. If you sleep there, the protagonist has a certain chance of being attacked by succubi or incubi. The dream manipulation option also works in such moments.
