I have just re-read the thread and we seem to have gone a bit off topic.
The forces imposed when racing are going to be a lot more extreme than us mere mortals are likely to experience. Part of the original question was “up or down when towing”. It then went on to “what is the tilt stop for?”
I think the up and down thing is down to personal choice and circumstances. In my case the engine manual says nothing about towing! Just leaving the engine up afloat. The tilt lock is only mentioned in relation to withdrawing the trim rods. I like the more balanced up position. Engine down most defiantly grounds the skeg on bumps, and the trailer balance is set up for engine up. It makes a hell of a difference to the nose weight.
Smaller outboards without PTT seem to have lightly constructed tilt locks, which could disengage over bumps. Red Fox’s manual implies this.
Hydraulic PTT should hold the engine anywhere, that is what hydraulics do. The lock in this case, I should imagine, is a safety device in case of hydraulic failure.
I seem to have got a green button, and do not want to do a Manos, so shall we agree to be confused together?