Viewer allows you to get immersed at an exact point and scale on a scene during play.
If you set the viewer as a target on the timeline and press play, you will be immersed in the viewer. To exit—press Stop on your controller.
You can switch between 3 modes of the viewer:
Point immerses you in the position and scale of the avatar figure at the exact height.
Standing Point does the same as Point but places your virtual head above the virtual floor at the distance of your real floor.
Area positions you relative to the actual tracking area of your VR setup, where the center of your tracking area in the real world is the center inside the viewer's area.