You can purchase QVS and Publisher independently and basic scheduling functionality is available with a QVS license.
Publisher is effective at providing reload and distribution functions. If you have a large number of documents, complex organization, or the need for complex distribution, then Publisher is probably necessary.
Publisher is highly effective at creating reduced data sets for specific groups, emailing output, managing complex security configuration, alerting reload failures, and distributing documents to disparate locations.
Hope this helps,