What is the purpose of the Disable Expired Relationships scheduled job?
End date alone does not determine if the relationship is 'active' or not. It will remain active until the scheduled job kicks in and makes it inactive. Examples include inherited memberships (membership by relationship). If you look in the advanced search you can see a radio option for active/inactive relationships. Its important to note anything in Civi that is using relationships to work out if it should carry out the action will most likely look for active relationships.