Well I was just curious to see what happens. I tried to run this https://www.microsoft.com/en-us/download/details.aspx?id=35
And I got a error "failed to download" and some log files popped up in system32. I checked DxDiag and I already have DX12 but I'm told by others I should not have ever got the error it should have told me "latest version of directX is already installed"
Microsoft Store - Download Center
The Microsoft DirectX® End-User Runtime installs a number of runtime libraries from the legacy DirectX SDK for some games that use D3DX9, D3DX10, D3DX11, XAudio 2.7, XInput 1.3, XACT, and/or Managed DirectX 1.1. Note that this package does not modify the DirectX Runtime installed on your Windows OS in any way.