Unreal Engine channel just published this tips & tricks video where they explain how to make use of Ray Traced Distance Field inside Unreal game engine. 

Ray Traced Distance Field Shadows enable you to generate high-quality soft shadow effects using 3D/volume textures, which store the nearest surface to a mesh. They can be used to great effect when dynamic lighting is required, and are generally 25% to 50% faster than standard depth-map-based dynamic shadows.

To learn more about the topic you can check the official documentation page.