good place to post!
It kinda depends how stiff/heavy the canvas is inside the lapels -- or if there is any interlining at all. If the the jacket has a heavier canvas, it might look bad if you added a higher button -- and tried to button it. Canvas (or whatever interlining is used) is cut so that the lapel roll stays in place. It has "memory" so it wants to roll to the same spot, usually to the middle button on a 3 button jacket or the top button on a 2. Additionally, the jacket collar is typically cut to match the angle/roll of the lapel.
So, if you buttoned the top button on a "3-roll-2" you basically force the lapel to roll up higher against its will, which can create weird pulls or bowing out of the lapels or make the collar gap. If the canvas and/or cloth is super light or there's none at all, like on a Barena or Boglioli K-jacket, it will be a easier to force close since there is no canvas structure trying to stay in place. Dry cleaners sometimes mistakenly press the lapels up to the top button. You can always try to press the lapels higher and see how it looks. Also, if you want to wear your tweed jacket like outerwear... pop the collar! and add a button to go in the lapel hole, that will keep out the chill.
a "3-roll-2" jacket buttoned the way up, courtesy of Yoox:
a true 3 button. lapels already rolled/pressed to the top button.
caveat: this mostly applies to 'classic' type jackets. also, the above may not be technically or, for that matter, grammatically correct. :-)
edited for clarity.
Edited by Parker - 8/8/15 at 9:57am