This is actually the core of the discussion really :
As you accelerate the first thing that happens is that the apparent wind moves forward, thus you need to (maybe) sheet IN.
I would say this sentence is imcomplete as
.... thus you need to (maybe) sheet IN or BARE-OFF
As the latter moves the apparent wind back to the original angle for which the sails were trimmed, avoiding any need to adjust the sheet tension.
Basically you can keep the apparent wind angle to the mainsail constant by changing the course of the boat and indeed sheeting the spi. That way you can optimize the performance while having only two controls in your hand instead of three. Of course when doublehanding your have 2 times more hands and can do more. Personally I only played the mainsheet traveller when 2-up to cut-off a rapid rising of the hull when I was too late steering.
Wouter
