Nearly anything we can do in the operating system with files and folders can be done inside of Lightroom. Gaining a proficiency with the Folders section will assist you in avoiding quite a few file/folder headaches in your workflow. Lightroom and your operating system are intertwined. What you do in one will impact the other.
It is important to remember that Lightroom approaches your file system in a much different way than your operating system. Lightroom is only concerned with where the files for your images are located. Your operating system, on the other hand, must concern itself with the location of every file and folder. That lets you show as much or as little of the folder hierarchy as you like to see. In our continuing example, suppose that we don't want to see Group 1's containing folder, Parent Folder. Easy! Right-click on Parent Folder and choose Promote Subfolders.
Remember that this is a database function and not a file system function. What that means is that when we promote subfolders in Lightroom it merely removes the containing folder from the Folders section hierarchy. Nothing happens in the operating system. The containing folder remains intact. This is for your organizational benefit.
After you choose to promote subfolders you are presented with the following warning dialog.
If you click on Promote Subfolders then Parent Folder will disappear from the hierarchy and Group 1 will be left. But now let's pay attention to the section of the warning I highlighted. What does it mean?
If Parent Folder only contains other folders then there's nothing to worry about. If, however, there are files in Parent Folder that are in your catalog and you promote the subfolders then those images will be removed from your catalog.
As I said previously, this is for your organizational benefit not your operating system's. If we go ahead with the promotion you will see that the image leaves the catalog but the file remains in the OS.
OK. Let's move on. Suppose you had to move your entire folder structure and all of its image files to another hard drive. Perhaps you had a drive failure or you are moving from an internal drive to an external one for portability reasons. Whatever the case, you used your OS and when you open your catalog everything appears to be gone!
This behavior is important to remember. Lightroom not only found the missing folder but it also traversed the folder structure and found everything else it contained. So, if you take care to put all your images in one folder hierarchy Lightroom can help you reconstruct the missing pieces.
Let's go in the other direction now. What if we want to move folders from one drive to another in Lightroom? If nothing from the other drive is in your catalog then that drive will not appear in the Folders section. Here is one way to do this (and there are others, so experiment). Click the + next to Folders and choose Add Folder.
You will be warned that this action will physically move files on the drive. Don't worry too much about the undo warning. All that means is the the undo command in Lightroom won't be available. You can undo this by moving things back to where they started.