In the past this extended error information was available in WinRAR, but not in SFX archives. Now this message is followed by a detailed reason like access denied or file being used by another process. For example, previously such archive would display "Cannot create file" message alone.
It is done to prevent possible attacks with inclusion of ZIP archive into the signature body.
Authenticity information may be added for additional security and RAR will store information on the last update and name of the archive. Even physically damaged archives may be repaired and an archive may be locked to prevent further changes.
It allows higher compression ratios than other PC archiving tools, especially on executable files, object libraries, large text files, etc.