Google's John Mueller said in a Google+ hangout on Friday morning at the 13:45 mark that when you move a site from one place to another, Google will typically crawl faster to pick up on those URL changes in a more expedited manner.
In addition, because of that, John recommends that when you do move URLs that you should do them all at once this way GoogleBot goes at it in the most efficient manner.
Here is the transcript of what John said:
Usually what happens when we see that a site is moving, we will try to crawl a little bit faster to pick up on everything and if you’re staggering it then essentially that means we see some some signs of a move but not a complete move. So if possible, I try to recommend moving everything in one go but if you can’t do that then, you can’t do that. There are always technical and organizational reasons for these kind of things so we can live with that too. Just make sure that when you have everything moved over at the end, make sure you set the change of address setting in Webmaster Tools so that we really know that the old domain has moved completely over.
Here is the video embedded at the start time:
It is interesting because Google has said time and time again, for big moves, sometimes you want to do it in chunks and not all at once to be able to make sure you can see how Google reacts to it.
Which is it?
Forum discussion at Google+.