I sometimes move up to E+ and it's equivalents when there are empty seats there. I only do it when I'm flying from A to B but when I've bought a cheaper A to B to C ticket. When I switch seats, I make sure put carry on in the F cabin on the way back to Y. It just fits in there better sideways and it's easier to pick up on the way out of the plane. I just find it easier in E+ to get my laptop out and write fake Trip Adviser reviews or watch a movie without headphones.