RE: Wind indicators
When I came from a multi hull background in the early years I did use telltales on my TC Spacer sail. And a long streamer off the top of the mast was also popular during those times. Mind you the centre of effort of the sail was all over the place whereas today with a good freerace sail or better, the sailor can (as mentioned by others) focus on what is ahead rather than the sail. How much to sheet in during gusts is something that becomes hard wired into memory as does lining up the forces when beating. Whether the rig is properly downhauled or outhauled can be felt and heard more directly than on a boat where the sheet is run through pulleys and cleats.