Depends. I arrived much earlier than scheduled off a transatlantic at LGW and had booked a cheap ticket to JER on Fly(May)Be. There were two flights out earlier than mine, went to the ticket desk, asked to change, they wanted £120, when I'd only paid about £40 for the original ticket.
I've worked in RevMan so I fully understand why the airlines don't want to change peoples' flights in those circumstances but knowing that the one I was one was full and the others not, I rang Exeter, spoke to someone in space control, who released a seat for me on the earlier flight, then went and checked in.
The point is that if the earlier flights are wide open and you have the potential to sell a higher revenue seat on a later flight, it makes sense to do so ..... but not to make too much noise about the fact that you will do it!