A differential backup contains all files that have changed since the last full backup. The advantage of a differential backup is that it shortens restore time compared to a full backup or an incremental backup. However, if you perform the differential backup too many times, the size of the differential backup might grow to be larger than the baseline full backup. At the first backup execution the catalog was not created yet, so the application will perform a full backup. The rest of the backups contain only the files that differ from the latest full backup.
Differential
Automatically make full backup
If the differential exceeds % of full backup size
In time, the size of the differential can outgrow the full version. For maximum efficiency, the size of the differential should be kept as small as possible. This option will trigger the creation of a full backup when a certain percentage of the full backup will be exceeded (default is 50%).
Make full backup when the differential exceeds
If this is checked, Backup4all will trigger the creation of a full backup when that custom size is reached (default is 100 MB).