Originally Posted by stargold

You really, really shouldn't. If you assign something now, you have the chance to get something better at the airport but also have the existing assignment to fall back on. If you leave it until reaching the airport, there's every chance that you won't like any of the seats that remain available by the time you get there.

There is neither any cost nor disadvantage in assigning your seat now. I strongly advise that you pick something that looks good for now.