Why you need Office 365 Data Backup:
Accidental deletion: This is actually the most common cause of data loss in Microsoft 365. If you delete a user, whether you meant to or not, that deletion will then be replicated across the network. A backup could restore that user, either to on-premises Exchange or Microsoft 365.

Retention policy gaps and confusion: Retention policies in Microsoft 365 are designed to help organizations comply with regulations, laws and internal policies that require that they retain or delete content; they are not backups. But even if you do rely on your retention policy in place of a backup, these retention policies are hard to keep up with, let alone manage. A backup provides longer and more accessible retention that’s all protected and stored in one place for easy recovery.

Internal security threats: When we think of threats to our business, we usually think in terms of protecting against external forces. However, many businesses also experience threats from the inside, and these issues happen more often than you think. Having a high-grade recovery solution mitigates the risk of critical data being lost or destroyed.

External security threats: Ransomware is becoming more and more sophisticated, and criminals are finding more ways to reach our users and deceive them into clicking a link that encrypts the entire organization’s data for ransom. A backup can easily restore data to an instance before the attack.