My environment: Oracle 12C Standard on Windows 2012 R2 server.
I have not yet set the ORACLE_BASE and ORACLE_HOME environment variables. But I do see the registry keys ORACLE_BASE and ORACLE_HOME under HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\KEY_OraDB12_HOME1.
My question: Is it necessary to have the environmental variables created too ? What Oracle utility or application component uses these environmental variables ?