Just to clear up, VMR is the Video Media Renderer and as I understand it is basically just the option to make full use of DX9 for newer cards or DX7 for older cards.
The option is there so people with older cards can still use MP, as long as they are aware that Timeshift and other more fancy functions may not work as well as could be.
There was a fair bit of debate a while ago as to which option should be the default.