The obvious advantages to 4K video are the resolution and then the ability to zoom in or pan across the frame in the edit when working in the smaller 1080 HD timeline. However, when you combine 4K video and the hybrid photographer it opens the floodgates for more creativity. I can pull a single frame and open it in Photoshop and alter parts of the video clip while allowing the other section of the clip to play normally, creating a surreal look. A still frame from the GH4 has enough resolution to be manipulated in Photoshop like any photo from a DSLR like my Canon 5D MkIII.
While recording, locking down the camera has many advantages. It allows for more creativity round tripping a single frame to Photoshop and back to Premiere Pro. I am able to create more effects like freezing people or moving people in reverse. Then I bring that 4K video (3840 x 2160 Pixels) into a 1080 timeline (1920 x 1080 pixels) and add the motion of panning and zooming in or out to look like the camera was moving to follow the action in the scene. Here is a link to a video with some simple effects added. This is just one example of what can be done to the athletes in this video. Note that only some clips were shot in 4K and final output is 1080 HD. Watch the video.