A. That depends on how much work you’re willing to lose. For example, if you backed up your catalog two days, and this morning you launched Lightroom, and your catalog was totally corrupted (this happens very rarely, but it can happen), then you’d only lose two days work. If you haven’t backed up your catalog in two months, then everything you’ve done since then (two months of work in Lightroom) would be lost, and you’d be picking up right where you left off two months ago. Usually, once a week is fine for most folks (again, a catalog crash is a very unlikely event, but so is a “water landing”). Still, if I wind up working on a big project, and...