When you break an item's permission inheritance, Limited access permissions are assigned to grant custom permissions in SharePoint.

SharePoint adds limited access permissions to all the site objects down the hierarchy, from the site collection to the object to which you added custom permissions.

It grants minimal permissions on all these site objects, so users can access the object you gave them custom permissions on.

When you remove the custom permissions on the object and restore the permission inheritance, SharePoint leaves behind the Limited access permissions, which do not allow further access to the user.

For example, suppose you break permission inheritance on a document and give a user Edit permissions. In that case, SharePoint will add the Limited access permission level on the site and library so the user can access the document without having complete access to the site and library.

If you remove the user's Edit permissions on the document, the user will no longer have access to it. Still, SharePoint will not remove the Limited access permissions on the site and library, and the user will no longer have access.

You migrate a site object and notice that ShareGate Migrate does not preserve limited access permissions from the source.

ShareGate Migrate does not copy the Limited access permissions.

SharePoint automatically establishes the necessary Limited access permissions as ShareGate migrates the effective custom permissions to your destination.

There is no benefit to migrating an unnecessary Limited access permission from a custom permission removed before the migration.

Because ShareGate Migrate does not try to copy unnecessary Limited access permissions during your migration, it successfully cleans your destination environment, and no further action is required.