Sonar: When to use?

So I've obtained my first sonar and tested it on a few now-annoyed people in the harbor. Now that I've been released from custody, what now? What circumstances do you find it useful in?

I would guess that, I obviously don't want to use it near warships. Merchants without nearby warships, from what I've read are okay. Is this correct? What situations do you find it most helpful in? What is the difference between the estimated and accurate options? Is accurate more likely to reveal your position?