You must create an Oracle Home User in certain circumstances.

• If an Oracle Home User exists, but you want to use a different operating system user, with different group membership, to give database administrative privileges to those groups in a new Oracle Database installation

• If you have created an Oracle Home User for Oracle Grid Infrastructure, such as grid, and you want to create a separate Oracle Home User for Oracle Database software, such as oracle

• Restrictions and Guidelines for Oracle Home Users
  Review the following restrictions and guidelines for Oracle Home Users for Oracle software installations.
• Determining if an Oracle Home User Exists
  You must decide to use an existing user, or create a new user.
• Creating an Oracle Home User
  Use the Manage User Accounts window to create a new user.
• Using an Existing Oracle Software Owner User
  If the user you have decided to use as an Oracle Home user exists, then you can use this user as the Oracle Home user for a different installation.