While in-place upgrades are nice, there are quite a few scenarios when you need to use the old-school deployment scenarios (new computer, refresh computer and replace compute).
Update September 25, 2016: Windows 10 v1607 added in additional support for third party disk encryption.
The Windows 10 Setup Upgrade process
When using the /Auto Upgrade switch to upgrade Windows 7/8/8.1 to Windows 10 (which migrates data, settings and apps) it does NOT support the following:
- Use a custom reference image
- Change from BIOS to UEFI or do other disk layout changes (change partitioning)
- Upgrade when having third party disk encryption (for now, may change depending on vendor)
- Note: In Windows 10 v1607 (and later), the new /ReflectDrivers setup switch allows inplace-upgrade when using third party disk encryption
- Upgrade when third party antivirus software installed (for now, may change depending on vendor)
- Upgrade between architecture (e.g. x86 to x64)
- Change the language (base OS language)
- Change to a lower SKU (the /Auto:Upgrade can only upgrade to the same or higher SKUs)
- Upgrade a "boot from VHD" system
- Upgrade Windows To Go USB sticks