For many people, putting all of their images into a single Lightroom catalog works just fine. When everything is in a single catalog, things are easy. All of your keywords are in one place and you can search among all of your images. For other people, however, one catalog doesn't do the trick. Some photographers have too many images for a single catalog and run into performance issues with tens of thousands of images. Others simply have a different workflow and a single catalog doesn't fit it. Lightroom makes it easy enough to run with multiple catalogs, but there are some things to keep in mind if you do so.

First of all, when using multiple catalogs, your all-important metadata is split up into multiple places. This means that if you want to consistent with your keywords, you'll have to remember your ontology in your head or on paper. Lightroom won't be able to help you remember that you use "clouds" and not "cloudy." for example.

Second, and this where things really get tricky, if you're using multiple catalogs and you reference the same images in multiple catalogs, it's incredibly easy to have different meta data and edits in different catalogs. If you are very structured in keeping your catalogs married to explicit subdirectories, you may not ever run into this problem. On the other hand, if you are in the heat of the moment you might find that you've imported a fresh batch of images into the wrong catalog and then move them into the right catalog. But, later when you are editing images in your first catalog, you might make some changes before realizing that you should have done them in your second catalog.

When this happens, you've got a mess to clean up. And let me tell you, even if you are normally very organized, this can happen to you. I've watched it happen with people I work with and I've even run into it myself. When it happens, it's not a fun situation to sort out. It takes a bit of juggling to make sure that you can grab just the settings you want from one, save them into XMP, and then sync those back up into another library. It's not how you want to spend a Friday afternoon.

If you are one of those who uses multiple catalogs, make it a point to make sure that you are in the catalog you intend to be in when you hit the import button. Double check yourself. The sanity you save may be your own.