Good point about controlling mainsail twist Jeff... I hadn''t thought of that. I suppose that the further aft the traveler is, the closer to vertical the mainsheet remains when eased, which would more effectively keep the end of the boom down to flatten the sail when you drop the traveler to leeward. However, with mid-boom sheeting, you''ll have a greater range of angular horizontal adjustment than an equivalent length of traveler track mounted for end-boom sheeting. That might be a minor advantage of mid-boom sheeting, unless the end-boom configuration has a wide enough traveler to enable the same range of motion.
Whatever; I''ll take end-boom sheeting any day, as long as the traveller doesn''t end up atop a "radar arch"!