Yes Rich, because of the angle of the slip, if I was to release the winch strap after before the boat was in the water, it would roll off and have a slight collission with the slip, even if it was partly submurged but not deep enough and I did the same it would still roll off. So, I fix a line from one forward cleat around the winch post and back up securing it to the other bow cleat, that way when I release the winch strap it doesn't roll off. I must say it can be scary when you release the winch strap as there is a slight movement whilst the line I have secured takes the strain. If that was not there I guess those lovely pneumatic tyres and greased wheels would quite quickly despatch the boat onto the slipway with a bit of a thud
Now, if I have got something wrong here, please let me know, maybe I am over cautious. I have in the past waded out when the boat is in deep enough water to release the bow strap but the novelty wore off. With the shape of the bow trying to release the strap from the bow eye whilst on the boat is not the easiest of operations, releasing the line attached to the cleats is a piece of cake.