The existing information for "Additional free space" (IMAGE_ROOTFS_EXTRA_SPACE) seems to be incorrect. It states that the maximum free space is 64GB, but I've been told this depends on the file system format selected. The variable's information in Hob should probably resemble the descriptions in the manual's Glossary. So for "Additional free space" it should say something like: "Sets extra free disk space to be added to your image. Use this variable when you want to ensure that a specific amount of free disk space is available on a device after an image is installed and running."
Sorry: changing "your image" to "the generated image" to keep consistency with the "Image basic size" description in bug 4355. So the information for "Additional free space" should say: "Sets extra free disk space to be added to the generated image. Use this variable when you want to ensure that a specific amount of free disk space is available on a device after an image is installed and running."
verified fixed on 676fd3f394a0c0576b63c77ed2184bf5f42c29b6