El Bunto:
Well other than for economy pax going from a 17.8"-wide 767 seat to 17.2" in the 787.
You're worrying about .6 of an inch in width, seriously?
The economy pax will have 34 inch seat pitch which is better than pretty much anyone, the space is very noticeable and I've sat in those economy seats.
Though perhaps this will be offset by the view from the windows when the FAs permit exterior viewing?
Cabin crew permit it constantly, only disabling the system when safety dictates. That's standard for this aircraft.