What kind of data would be lost if only differential backups are used without regular full backups?

Using only differential backups without regular full backups can lead to the loss of all data since the last full backup. This is because differential backups only store changes made to the data since the last full backup. If there is no full backup to restore from, all the changes collected in the differential backups would be unusable without the foundational data provided by that original full backup.

In the event of system failure, data corruption, or loss, having only differential backups means that any changes made since the last full backup would not be recoverable if that full backup is not present. Therefore, to ensure complete data recoverability, regular full backups are essential in tandem with differential backups. This highlights the importance of a comprehensive backup strategy that includes both types of backups to mitigate the risk of data loss effectively.