Some examples, first my tired old S2... You'll note the main on this boat is 25+ years old... probably has effectively though about 10 seasons on it.
Red circle is draft, note its probably in the first 35 percent, well forward of middle. Also note, green, is my flattener... The flattener in green will tension the leech, and flatten the WHOLE sail, but primarily the aft middle section. Note I have none attached.
Outhaul will flatten the aft lower section some, but more it'll reduce draft across the lower half of the sail.
Blue is my cunny, flopping in the breeze... There are no wrinkles (what my father used to call "scallops") in the main. Scallops are necessary when the winds are lighter (than shown) to provide a deeper, fuller main (or genoa)...
Ok so now I'm going to pick on myself. This was my first race with this boat, and my first race this season... winds were lighter when we started, winds grew by about 5 knots during the race... this was us just before the finish line... Note the newly formed "scallops" in the genoa? YEP, I've since figured out that the rope clutch is slipping on my genoa halyard (I use a clam cleat now while racing). It doesn't take a rocket surgeon to see that I've completely dumped my mainsail, and it's backwinding in this picture... what isn't as obvious, is my mainsheet is full on, my traveler is dropped my backstay is full on... I'm seriously overpowered (no thanks to that genoa). If you notice hard enough, you'll be able to tell too that my draft has slipped back considerably.. THIS is where the cunny is required. If I had applied my cunny that draft could have been moved back forward where it belonged and I'd be able to help this situation some (but only AFTER I slid my genoa car back a notch, and secured a tighter genoa halyard). I had new crew, that was inexperienced, so some things got neglected, and of course it was JUST the 2 of us... Not making excuses I'm a bit more thorough when I race this beast now.
Now contrast that with THIS picture of my Capri 25 with crisp laminate sails, loose foot, and honestly the sails just fell into good trim... Note there was wind disturbance from the darned topping lift which I later corrected by removing the topping lift all together, and replacing it with a boomkicker. But this was excellent trim, both genoa and main, upwind right at the start
Don't believe me.. see if you can see much curvature difference between the genoa leech and the main? Because you can actually see them both for about 1/3 of the height in this picture. I was quite proud of this start, as I was making time, realtime with the S2 7.9 which is admittedly a faster boat than the Capri 25... and the sailor I was able to keep pace with is one of our best sailors.
I like to use this next picture as my favorite ever for the boat, though because it encompasses good trim cracked off slightly from close hauled and everything is set pretty well perfect (a rarity for us).. Hard to tell draft, but outhaul is set correctly, sheet is correct, vang is correct, genoa halyard isn't too tight, headsail is set for maximum power, backstay is off (for power), and we're nearly at hull speed... just a nice picture... I get pictures of my own boats, and then as I stare at them I learn to hate what I've trimmed wrong. Am I the only one? Anyway, I used to have a copy of this picture that I circled everything and critiqued it still, but its one of the few I can find the least fault with while we were racing.