Lightroom 4 only really needs the LRCAT file (and maybe some settings files), but LR4 is creating Previews.lrdata folders on my system. It takes a long time to do backups with all the extra files and folders. Do I have something checked causing all of the extra files and folders? I looked in the prefs and catalogs settings and don't see anything unusual.
Even if I delete all of the preview folders, LR immediately starts rebuilding them.
#1. "RE: Lightroom 4 Preview File Folders" In response to Reply # 0
I'm sorry but I think that's how Lightroom works. It creates a cache (preview) of the images for speeding up the user interface (UI) and all the processing. Without them, it would have to read a RAW file and apply all the changes every time you select a different image.
Consider the filmstrip, for example. It shows maybe 20-30 images. To show the images in the filmstrip when scrolling left and right without any pre-processed, readily available data would make your computer very, very busy and the UI very, very slow.
You can configure the maximum size allocated for the previews and how long Lightroom keeps the previews (for images you haven't viewed for a long time). I believe the default max size is 1 GB but in order to speed up things in Lightroom, it should be something like 10-20 GB to reduce the need to recreate the previews - depending on your usage.
You can also configure the size of the previews while importing and also in general (i.e., in preferences). The larger the preview the faster Lightroom shows the final image and minimizes the appearance of the "Loading..." text.
I would solve this by configuring the backup software to skip the preview files, either by excluding the file name or the folder. These can be discarded since they can be always recreated.
Actually, you HAVE to recreate preview images when you upgrade Lightroom. Otherwise, you'll see pixelated versions of your images in future versions. At least upgrading from Lr 3 to 4 caused this for my images.