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what''''s up with sail twist?
I will try to answer your last question first, specifically:
"can anyone explain this to a newbie?"
Imagine you have a tall pole with a bunch of long streamers or pieces of yarn attached at regular intervals from top to bottom. Imagine that you are standing with the pole in front of you. If there is no wind, the streamers just hang down. If the wind picks up then the streamers will begin to fly/float/flap along the direction of the wind. Imagine that the wind is coming directly from the side (lets say your left side), then the streamers will be blowing out to the right. Now we add a little more complexity to the picture, because when the wind blows, it is blowing slower closer to the bottom (whether water or ground) because of friction, and faster as you go up. So, in a light breeze, the low streamers might barely move to the right, while the streamers up high are flying out quite well (By the way, at very high wind speeds, there is still a difference in wind strength as you move up away from the surface, but the difference is small relative to the overall wind speed, so that in a gale, all the streamers are blowing out straight).
Now suppose the wind dies, and you start moving your pole forward. The streamers begin floating back. If you move the pole quickly (forward) through the still air, then all the streamers will equally fly straight back (since the pole is moving forward at the same speed along its length).
Now, suppose that while you are moving forward, the wind begins blowing from your left. Now the streamers that were floating backward because of the motion of the pole forward through the air, are now also being blown toward the right. And the ones near the top of the pole are being blown by a stronger wind than those at the bottom (because of the friction at the surface, the wind speed is slower). Suppose at the top of the pole, the wind speed is equal to the speed at which the pole is being moved through the air. The top streamers would be floating out halfway between ''right'' and ''back'' (45 degrees). The streamer at the bottom would be pointing more toward the back, because the ''wind'' caused by moving the pole forward would be stronger than the wind blowing naturally from the left (which is not as strong at the surface than it is up high, where we said the two winds were equal). So, if you look up your pole (or mast) you would see a set of streamers (or you can imagine them as wind vanes) that are pointing in a gradually shifting direction as you go upwards from closer to straight backward near the bottom to 45 degrees at the top. This should give you a picture of the what the wind appears to be from the perspective of the leading edge of your sail (we are ignoring the problem of the pole/mast itself interfering with the wind).
As you might know, you want to trim your sail relative to the wind direction. As you have seen, though, the wind direction at the top of the sail is a little different from the direction at the bottom. Having sail twist allows the sail to be trimmed appropriately from top to bottom (the top of the sail would be at a greater angle to the centerline than the bottom of the sail, which would be closer to the centerline).
Of course, you don''t always need or want sail twist (or the same amount of twist) for optimum performance in different conditions. In very high winds, the true wind is blowing much harder than the "wind" caused by the boat moving through the water and the difference in speed and direction between the top and bottom of the mast is much smaller as compared with the overall wind speed (meaning the difference is negligible) and you might be mostly concerned with flattening the sail as much as possible to minimize heeling and avoid being overpowered etc. This is admittedly a simplification, as all sailing theory and discussion is necessarily a simplification of the continuously varying conditions actually involved in sailing a real boat in the real world.
Now, if you are still with me, I will try to answer your original question:
"is sail twist an important element to sailing or is it just fine tuning"
This all depends on what your sailing abilities are and what you want to get out of your sailing experience. For many, part of the joy of sailing derives from understanding and controlling the boat as precisely as possible to optimize sailing performance. That is, the joy of sailing comes from the joy of sailing well. I should add that in some cases, having a thorough understanding of the many and various factors involved in handling a sailboat in a variety of conditions can spell the difference between life and death (though sometimes that too can be a matter of simple chance or fate). BUT, for many, the joy of sailing comes from being out and moving modestly through the water from one place to no particular other place and being with friends etc in not too hazardous conditions. And if that is part of the experience you cherish, then I would say that you can hoist your sails and trim them modestly well and relax and have a good time and not be particularly concerned about whether you have just the right amount of twist in your sails. You can still move through the water at a reasonably fast pace by getting the basics right. Later on, if you want to do more, there is always room to improve.
I hope this answered either or both of your questions