Microsoft has now enabled the Retpoline Spectre mitigation feature by default in Windows 10 version 1809 (October 2018 Update) for better performance. Microsoft released mitigations for the Spectre vulnerabilities they caused a performance hit on older computers. To realize the benefits of the feature, IT Admins can enable it on servers following this guidance. For users who currently have Spectre 2 mitigation enabled and. you are using an older computer, you should now feel a performance improvement with Retpolipoline enabled.
Source: https://www.bleepingcomputer.com/news/security/windows-10-spectre-2-mitigation-now-uses-retpoline-by-default/