From what I understand, Lr builds these files when needed, So, if I delete them, Lr should rebuild them when I open a folder that I haven't edited for a long time. I do have a finished JPG of all the edited files. I could recover over 6GB of space by deleting them. Folders that I haven't used and may not open them in Lr for a while, I see no reason to save these previews.......My external hard drive has 485GB free on a 1.8TB drive. Not sure if setting a 30day limit in the setting is long enough. Advise please.