Someone takes another person's car without permission and returns it. The cause of action is for conversion. If the taker also destroys the car, trespass to chattels would also be available. If the person from whom the car is taken is merely holding the car for the true owner and the car is not destroyed, then the person from whom the car is taken does not have a cause of action for conversion, but the true owner would. If the car is destroyed, the person from whom the car is taken would have a cause of action for trespass while the true owner would have an action for conversion or trespass.
Someone keys someone else's car slightly, causing an insignificant amount of damage.
The true owner would have a cause of action for conversion and there would not be one for trespass to chattels. A local restaurant stuffs a landowner's mailbox with flyers making it difficult to use. The cause of action would be for conversion. Trespass to chattels would be available if this intermeddling caused substantial damage. A reporter makes use of information from a senator's files.