I didn't find it super clear in the article, but I have read in other places, that it's the lowering the weight down in any movement that makes it work. So it doesn't have to be super heavy, just come down slow and fatigue the muscles.

So I guess if you use lighter weight, it can go up faster. But yeah, it's not clear on how any of this saves time

To be honest, I think the real takeaway is that ANYTHING you do works as long as it's consistent. I've seen multiple studies that show that different rep ranges, heavy vs light, etc all show good results if ya just keep doing it and make it a habit.

I personally think the heavy stuff is for younger joints, lighter stuff is for older joints. I used to be a huge advocate of heavy, but I have seen too any older lifters who went heavy for too long, walking around in constant pain. The lighter weights guys seem to avoid that.