After yesterdays release of Lightroom mobile, I want to reiterate that when you sync a collection of images from Lightroom on the desktop to Lightroom mobile we are syncing Smart Previews – not the entire raw files. This means that you should not think of Lightroom mobile as a “backup solution”.
There are a number of reasons for using Smart Previews in today’s workflow including; bandwidth, speed, performance, and storage space. So although you might have thought that Smart Previews were only useful for working with off-line files, now you know that they were designed for and specifically optimized to be used on a mobile device.
And don’t worry, Lightroom will create Smart Previews for the images that you choose to sync automatically, so you don’t have to do a thing.