Only if the engine had no built in way of being totally imobilized. Older outboards that had no Hydraulic or mechanical locking system. another place, the Original Mercury Power trim for example, once the engine was all the way up, you had to lift is some more by hand and flip over the trailering lock, The motor could still bounce up and down. there a transom saver was a good idea. Later Power trim systems, the engine could be immobilized or locked in position on the transom bracket and these cases a Transom Saver can damage the Transom. If the boat is not completely immobilized from moving on the trailer, and/or the Trailer is not compressed lengthwise(bowed) when the boat is strapped down and the so called Transom saver is hooked up. If the boat moves back or forward the slightest or the trailer un-bowes then all that force is directed to the Transom.
On my I/O I use what look like partial pipes that go over the extended rams on the outdrive and lock them in place with the hydraulics. On older boat with OBs, I would engage the tilt.trailer locks on the engine, secure them with the Hydraulics. Motor stayed rigid and transom never had any issues.
