In the video, you mention seeing other riders doing this, as well as others who have posted in this thread. I see it as well and agree, that most people do it for the wrong reasons.
However, if and when you have slippage or debris on your tires and you are leaned over in a corner, you maintain a steady throttle and ride it out. It takes A LOT OF SELF CONTROL to maintain the course of action. Most people tense up, back off on the throttle creating extra load on tires that are already lacking traction, and end up low/or high siding as a result. Hell, even Kieth Code mentions it and I disagree with a lot of what he has to say..lol He shows a demo of it in his Twist the Throttle 2 video on a bike with outriggers.
I have lost traction many times for various reasons in my riding career. Doing perfect demos for students in wet conditions in a parking lot where you have oil, antifreeze, gravel, sand and you do exactly what I mentioned while in a corner.
If you are in a straight line after running over crap on accident, you don't swerve quickly. That would obviously be stupid. Though you can swerve in your lane aggressively, though smoothly, and be fine. What the hell do you think you do when you are on a freeway, wait till you find a long sweeper or overpass? No, you try to clean that crap off asap.
So I say, before you go assuming a rider is doing exaggerated swerves to warm up their tires, you might be wrong about it as there are other reasons to do it..one of them not being to warm your tires up.