Not necessary, it's just some sort of theft deterrent, at least never have bolted any of my horses as are removed from boat at days end, just match both clamp eyes to be front of each other and tie a rope betweeen them. It's really very stupid to just adjust clamp tight or even secure a rope to engine, have seen brand engines fall into the blue forever.
I knows of several cases of motors coming off boats during operation, generally while making a turn. We lost a trolling motor while trailering the boat ourselves. Until the motor clamps make indentations in the transom, this can happen.
On one boat, I screwed a piece which fits right above the motor clamps to prevent this. It is very easy to prevent such a loss.
I have one of those self coiling short cables. I may put an eye bolt in the transome and loop the cable around the motor mount and padlock it. Might keep it from disappearing when pulled up on shore this winter.
Keep the cable short enough that the powerhead does not enter the water with the motor running. That is why I favor the strip above the clamps as if it slips off horizontal, it cannot slip completely off the transom. The prop would destroy the hull almost immediately because of the sponsons.
You can purchase one of those locks which slips over the clamp screw handles if you plan to leave the boat unattended.
