its useful because this allows the cpu to use vram as normal ram and the gpu can use the normal ram as vram.
without streaming coping data between spaces.
the workload in dx12 is different they drop shader based light effect and go for light raytracing light effect.
the ray-tracing will only be in the light effect all others are still raster rendering.
maybe they do object collision calculations also via ray-tracing.
directX 12 is an raster+light raytracing mix.