Sailing for performance means going as fast as possible under the circumstances, whether it's point to point, around buoys, or just reaching a harbor mouth before sunset. We usually associate sailing for performance with racing, while in "Cruising" or "daysailing", sailing for maximum performance is not usually the focus. However, maximizing performance can become very important when getting home in dying wind, for example, or sailing against an adverse current.
Therefore, the discipline and knowledge of sailing for performance is not just for racers, it's for any sailor who wants to maximize comfort and safety.
So how do you optimize performance anyway? In beginning sailing texts we learn that to sail to windward, set the sails all the way in, then steer to where the jib's telltales are streaming aft. To sail on a reach, aim the boat where you want to go, then adjust the sails to where the telltales are streaming aft. Simple, effective advice, and mostly true.
When is this simple advice most ineffective? I've seen beginning sailors with the sail (especially main alone!) all the way in, pointing very high, and going nowhere. Actually, not nowhere, they are actually going sideways very, very slowly. With no flow over the centerboard and the sail strapped in hard so there is almost no sail force aimed toward the front of the boat, the boat can drift sideways, stuck with a near-luffing sail and a stalled centerboard.
I was at the Windsurfer national championships on Lake Michigan in the early 1980s, and was sailing upwind between races in 8-12 kt of wind. To leeward of me, about 30 feet away was Bobby Wilmot, then Australian national windsurfing champion. We were going about the same speed -- mostly. Sometimes, for no apparent reason I would, in the span of about 5 seconds, lose about 1/2 board length to him. Then, we'd resume going at the same speed again for maybe a minute or so. This pattern repeated itself over and over.
After a few minutes of this, I started to realize what was happening. As a gust reached us, I would respond appropriately, heeling slightly to weather and heading up slightly to maintain a barely-planing speed which optimizes windward performance in that wind speed range. However, when the gust ended in a lull, I didn't reverse the process right away, but instead would lose speed for a bit, then get it back together and accelerate. I was sloppy enough to lose about 1/2 board length to Wilmot every time this happened.
The key to fixing this problem was to develop a more keen sense of boatspeed; when I lost a bit of speed and then worked to get it back, I lost ground. If I could react and fall off slightly when the lull began, I could keep speed more constant and sail more like Wilmot was sailing.
I learned to race at the Cal Sailing Club in Berkeley in the late 1970s. On Sunday mornings, we raced Lidos around a semi-sheltered corner of the San Francisco Bay. I understand these club races continue even now, 40 years later, although the Lidos are long gone. There was a Finn fleet that used the same location, and occasionally we would invite the Finn sailors to join us in the Lido racing, rotating into our boats.
They kicked our butt, almost every sailor, almost every time. I was amazed at how much more proficient these Finn guys were in our boats which they never sailed otherwise. One race when I wasn't racing, I was walking on the shore not far from the weather mark, and watched one of the better skippers round the mark, followed by one of my peers. The Finn skipper lost only a small percentage of boatspeed rounding the weather mark and falling off to a run, while my clubmate lost about half of his boatspeed making the same rounding 5 seconds behind.
Again, the key to fixing this problem was to develop a more keen sense of boatspeed, what we do to kill boatspeed (sudden, sharp tiller motion works great for this!), and what we can do to preserve our speed while turning, for example heeling the boat to take advantage of the tendency of a boat heeled to windward to fall off.
Once again, getting sensitive to where I might be losing speed helped developed my awareness of how fast the boat is moving through the water, and how I might be able to slow it down less.