I know Lightroom creates previews and keeps them in a folder \Pictures\Lightroom Catalog Previews.lrdata (at least in the Windows version of Lightroom). At present my "Previews" folder is over 1.6 GB in size. These are "Medium" quality previews; the 1:1 previews are kept for 1 week only. From what I have read, Lightroom will recreate this folder if it is missing. Is this true? If so, I will discontinue backing up the LIghtroom Catalog Previews.lrdata directory. Of course I always back up the catalog itself (Pictures\Lightroom Catalog.lrcat ).