It's less any specific missing features and more the confidence that I'll literally never run into a missing feature - the things you almost never need, until you do. E.g. upcasing a Turkish string, or printing a number that does the correct thing with `,` and `.` in the user's current locale. PowerShell's support for ACLs is also hugely helpful - being able to do the structured-data thing with the icacls command would go a long way.