Microsoft 365 services provide a data retention period of 30 days.
Backups will be needed for the following reasons:
Email data is deleted and this is only noticed after 30 days.
Online data storage using OneDrive or SharePoint is deleted and this is only noticed after 30 days.
Data in Microsoft Teams.
Azure data.
This can happen accidently or maliciously by staff members leaving, hackers and viruses.
Unlimited storage space.