Originally Posted by lallyr
I have never had any success with checked in luggage. You have a much better chance to pick up your luggage and then request a earlier flight when you check-in again.
I would agree with this advice.
Once luggage is checked through to a final destination, airlines are hesitant to move you to another flight because of security reasons. You should travel with your bags (although it is fair to say this does not always happen and you discover this once you get to your destination but that's another story...).
If an earlier/later flight is not full it really depends on how you ask and who you ask I guess. If you want a guarantee of flexibility then buy a changeable ticket.