The main idea is to be able to load an a video with a progressive quality. Instead of exporting a video in different resolution to be able to broadcast it no matter the connection speed, the video stream include a quality dimension in addition to the time. When loading the video, the priority is given to real time and depending on the downloading speed, the quality will adpat.
This allow lossless compression since the quality will always be the best for the available bandwith.
Instead of storing a video in different qualities, you get only one file that does it all, meaning consequent memory gain.