The 787 was originally intended by Boeing to have eight abreast seating in Economy.
The nine abreast seating on this aircraft means one, more, or all of the following:
Seats are narrower than average.
Armrests are narrower than average.
Aisles are narrower than average and aisle seat passengers are prone to being bumped.
Window seats are set tight to the fuselage.
Seat with solid armrests
Seat with some positive attributes
Seat with both positive and negative attributes
Seat negative attributes
Seat with some negative attributes
Seat at a bassinet/cot position