Those clips are one of those things that certainly aren't bad, and they would protect the drive if you were on the road and the hydraulics failed. On the other hand, how often do the hydraulics fail? The vast majority (like 99%) of boats I see towed don't have them, and I don't know that I've ever read a first-hand account on iboats of someone whose drive dropped and dragged on the road.
I've considered them at various times, but it seems like just another thing that might be overlooked when launching the boat. If I were to get them, I'd most likely use them mostly on long highway trips.
I honestly don't know if they'd damage the hydraulics if you were to forget them and try to lower the drive. I wonder if maybe the rams would exert enough pressure that they'd pop the clips off, but that's just conjecture.