A lot of the clever tricks employed to get effects like reflections, ambient occlusion, soft shadows and GI effects using rasterization are 'hacks' with a lot o

A lot of the clever tricks employed to get effects like reflections, ambient occlusion, soft shadows and GI effects using rasterization are 'hacks' with a lot of edge cases and artifacts. They're not terribly robust. Ray tracing let's you get better quality with fewer artifacts because there's less 'cheating' going on. You can get better quality in more situations with less manual tweaking, if you can afford the performance cost. Artifacts around the contact points of shadows and reflections and artifacts for reflections and ambient occlusion of off screen objects are places where ray tracing can give much better visual results.