What is the correct use of the traveler anyway, up to my understanding, its is to improve the trimming of the sail depending on wind direction, moving it downwind as the wind moves further aft. If the traveler is two short, the leech would make a bigger curve and the foot would go up a bit (at least on mine that is boomless), which in my opinion depowers the sail, not the opposite, it also would produce more heel.
(I understand what jake says, but I was thinking of easing the traveler and at the same time pulling the mainsheet, so the sail angle would be the same)