You may be using a lot more hard drive space with Lightroom than you need to be. There are three major opportunity areas: catalog backups, 1:1 previews, and deleting rejects.
My Lightroom catalog is about 500 MB. (To see how large yours is, go to Edit>Catalog Settings on the PC, or Lightroom>Catalog Settings on the Mac. The size is listed on the General tab.) If I do a catalog backup once a week, that is 26 GB of catalog copies that I am adding to my hard drive every year. If I do a backup every day, that is 182 GB per year! It is important, therefore, to go in and clean out old backups. I like to keep a few backups in case my catalog already had corruption issues during my most recent backups. I keep one a day for a week, one a week for a month and one a month for a year.
If you are not sure where your backup catalogs are, next time Lightroom prompts you to back up your catalog, note in the dialog where they are going. In Finder or Windows Explorer, navigate to this folder. You will see a folder for each date — delete these date folders.
Lightroom creates and saves 3 jpeg copies of each of your images in a preview folder (or file) in the main catalog folder: a thumbnail-size jpeg that you see in Grid view, a screen or standard size jpeg that you see in Loupe view, and a full-size 1:1 jpeg that is used when you zoom in on an image in the Library module. The 1:1 previews in particular can take up many gigabytes of space on your hard drive, depending on how many images you have in your catalog.
You can have Lightroom throw away the 1:1 previews a day, a week, or a month after they are generated. Go to Edit>Catalog Settings on the PC or Lightroom>Catalog Settings on the Mac, click on the File Handling tab, and in the Automatically Discard 1:1 Previews drop down, choose a length of time that covers how long it typically takes you to work through a shoot.
So what if there is no 1:1 preview available, and you zoom in on an image? Lightroom simply creates a new one — you will see the message “Rendering Larger Preview” on the image as it does this. Depending on your system, you will most likely find this quick and painless.
When you delete images from within Lightroom, the dialog gives you two choices — Remove and Delete from Disk. If you choose Remove, you won’t see your images in Lightroom, but they are still on your hard drive taking up space, in most cases unneccesarily. I suggest that for many if not most of us, Delete from Disk makes more sense — this removes them from Lightroom and deletes them from your hard drive.