3703357 - What is the difference between "Update Only" and "Update Details" operations when importing user to group mappings?

I want to import User-to-Group mappings using the Import User to Group Mapping Data (Consolidated File) task, but I see two similar options: Update Only and Update Details.

I am not sure what the functional difference between these two operations is or which one I should use for my scenario. In some cases, users were unexpectedly removed from groups after the import, while in other cases existing group memberships were not updated as I expected.

entitlement loss, access drift, membership reset, assignment impact, destructive update, partial import, sync risk, authorization change, access persistence, privilege scope, identity sync, permission drift , KBA , BNS-ARI-CP-CORE-UM , Core Administration User Management , BNS-ARI-CP-CORE-IEX , Core Administration Import/Export , How To