For five decades, Dallas-based budget airline Southwest made its reputation on its unique open seating policy. On Tuesday, Southwest Airlines officially inaugurated its new assigned seating policy, the last in a suite of changes that moves it closer to the mean of airline operations. Taken by itself, the new policy, which breaks passengers into boarding groups and loads them according to seat location, should be more efficient. But the new Southwest Airlines process has some catches that will gum up the works. Just the extra legroom seats, which rolled out last May, should deliver an extra $1.5 billion annually by next year, Southwest Airlines president and CEO Robert Jordan told investors last fall.