In the post about gybing, Gary mentioned wanting a lower block that had a built-in cam-cleat and I agreed with him.  I have transferred my comment here as it is not really about gybing the sail, since I do not uncleat the sheet when gybing.  My attraction to the cam-cleat is to control the sheet when reefing or furling.  As I slack the halyard with one hand I like keep a bit of tension on the yard hauling and throat parrels, pulling them through a pair of rope clutches with the other hand.  I have to stop and pull in some sheet every now and then, to prevent it going in the sea.  Having a cam-cleat on the lower sheet block would make that action a lot quicker and neater.

I have called this thread sheet systems so that other aspects of setting up and controlling the sheet can be included.