You use this flag if your application will only call methods of Direct3D 11 and Direct3D 10 interfaces from a single thread. By default, Direct3D 11 and Direct3D 10 are thread-safe.
By using this flag, you can increase performance. However, if you use this flag and your application calls methods from multiple threads, undefined behavior might result.
Minimum supported client
Windows 8 and Platform Update for Windows 7 [desktop apps only]
Minimum supported server
Windows Server 2012 and Platform Update for Windows Server 2008 R2 [desktop apps only]