SharePoint Online Permissions Auditing
Currently auditing site collections (including folders, lists and documents) access permissions requires global admin rights. A Global Audit admin account should be created to allow access permissions to be fully audited without the ability make changes.
The ability to view audit logs does not allow an auditor to obtain a snapshot of all existing access rights for a site collection, only specified activities over a limited period of time.
Chandrashekar Kollipara commented
This is really essential where you have multiple site owners modify permissions, especially removal of users from site