Youtubers are so long winded so they can fill the >10 minute mark so they can add more commercial content and get more revenue.
Speeding up content isn't really multitasking, its just trying to fit more into the time you are wasting anyway. I doubt it feeds productivity, instead it feeds listlessness and short attention spans. But on the whole I appreciate it and use it whenever possible. My TIVO boxes have a 1.5x playback function and I feel I lose very little on news or other shows filled with mindless blather. I generally don't do this for movies or comedies where its nice to sit back and enjoy what they have created for a time.