Hello,
When you check the box for "Create a single .EXE for this package", it would creates a single installation executable file.
When you uncheck the box for "Create a single .EXE for this package", it would create an unzipped package with .msi package setup.
Single executables are not supported with an Active Directory group policy installation or auto-upgrade by using the Symantec Endpoint Protection Manager.
Symantec Antivirus.msi Package is very useful in many issues where Customers often face issues like "The Windows Installer service could not be accessed"
Hope that helps!!