Everyone knows that if you sail a little wider tacking angle you must cover extra distance, and so need to be going faster. However what most people don't know is that if you lay off the apparent wind say 5 degrees, and as a result pick up a knot or two, that you are laying off the true wind significantly more than 5 degrees because of the apparent wind shift from the extra speed. In the 28 deg 10 knot true wind case, suppose you are pinching at 6 knots BS. Your true wind angle will be 44 deg, your VMG 4.3. You decide to lay off 5 degrees apparent wind and pick up to 8 knots - a significant increase, but many boats will do something like that. And you think you have only given up 5 degrees to do it. However you true wind angle is now 59 degrees - not the 49 you were expecting - and your VMG 4.1. You thought you have given up 5 degrees on course but in fact gave up 15 degrees, so even the 33% increase in speed will not recover the extra distance sailed.