The Vault lets you do three kinds of backups. A full backup copies all the files on the disk. It often takes a long time because a hard disk stores a lot of information. It should be done initially and then from time to time whenever a clean copy of everything on the hard disk is desired.
Backups should be done frequently, but the files on a disk change slowly. Most of the time, only a small part of the hard disk changes between backups, making it redundant and wasteful of time to always do a full backup. A daily incremental copies only those files that have changed since the last full or incremental backup and is generally quite fast.
After many daily incremental backups have been done, the incremental backup disks may contain many copies of frequently changing files. This takes up valuable disk space and makes it harder to find the most recent version of a file should it need to be restored. When that happens, a cleanup incremental backup can be used to ``clean up" and reorganize the several disks full of incremental backups, writing out the current version of every file that has changed since the last full backup (rather than since the last incremental backup). If the incremental backups still use too many floppies, it is time to make another full backup.