Does Adobe Downloader download only differences when run a second time to the same destination?

I'm considering adopting the Adobe Lightroom Cloud offering.  I am trying to find out a few things first to maximise the 7-day trial before I start it.

I'd like the option of periodically downloading everything - and it seems I can do that using the Adobe Downloader.

If I have a large library, and I download a second time using the same destination folder, will the program download only differences, or does it always download the entire library each time?