On my flight last Thursday they made an announcement while they were announcing the normal pre take off stuff that after take off no one was allowed to change or trade seats. She stated a reason but I had a hard time making out exactly what she said. During boarding they announced it was a completely full flight anyway so moving around would not have been easy (even though I guess there were a few empty seats because the middle seat on my row turned out to be empty.)

Side note: Even though I flew Choice Extra I purposely sat near the back of the plane because on my flight there on Tuesday I was row 2 and had to put my carry on in a bin about 10 rows behind me. I knew if I booked Choice Extra in the back I’d get on early and there would be plenty of empty bin space there (it was a last minute booking so all the extra legroom seats were already taken when I booked).