The security role privileges are synced when a record is shared or assigned to another user. For e.g. when a User A (Sam) owns a record and other User B (Rhea) has only user level access, then Rhea won't be able to see the records owned by Sam in SharePoint.
For instance, records visible to Sam are:
Records visible to Rhea:
Now Sam shares the record with Rhea.
After the records are shared with Rhea she will be able to view the records owned and shared by Sam in SharePoint.
Now due to some business requirement Sam assigns the record to Rhea.
The record will not be visible to Sam anymore and will be assigned and visible to Rhea in SharePoint. Visibility of records to Sam after record is assigned to Rhea:
Now that record is assigned to Rhea, visibility of record to her: