The rationale behind "platform_default" relates to what we put in the default config file in the RPM. If enable/disable are the only options, then as soon as the first version ships with "disable" as the default, affected systems will *never* switch to being enabled by default unless the system administrator changes it.

By contrast, if we put "platform_default" in the default configuration, then inattentive sysadmins could theoretically eventually have their defaults switched to "enable" at some point.

We don't know yet if we'd ever upgrade the "platform_default" setting, but I think it's worthwhile to retain the option.