If done right it can help. Especially if the lower unit is way too low. With fixed jack plates and for the boats I run which are a little different that the CS J16, the sweet spot is just high enough to have a little bit of cavitaion while jumping on plane but a good hook up once it reaches WOT.
A jack plate can actually make steering torque worse. With less of the lower unit in the water its harder to compensate for the rotation of the prop. Still a well balanced boat and properly mounted motor can be set up with a jack plate so that their is little torque. For boats with nasty torque problems a Torque Tamer is usually the last resort to fixes the issue.
Good luck!