Why do you not see it, letting water full drawdown each pour in multiple pours, advised? Are there downfalls to doing it?

Today, with a Hario Switch, I did: http://www.youtube.com/watch?v=xKqWYmjXoag

It is a Hario Switch recipe of four pours, including bloom, with each pour at a 4:1 ratio, for a total ratio of 16:1. You poor the 4:1 bloom with Switch open, stir and then after the bloom drains, make the 2nd pour, also 4:1 but with the Switch closed. Then let it sit 15 seconds, open switch, letting it fully draw down, then close switch and repeat. On last pour, after opening Switch you do swirl. He says he gets mid 25+% in extraction doing it.

I did it today, at a medium fine grind. No clogging, which I thought might happen since I ground fine for normal pour-over but it took 5:30 minutes for a ~24g dose. It never clogged, remaining a stream until end of last pour.

The coffee was very good - very sweet, rich and smooth. It had a noticeable aroma which my coffees never have and the aroma was a sweet aroma too. Also it had more oil sheen on surface of poured coffee which my coffee does not have normally. Based on those things, I assume I also got a high extraction.

Since there was no clogging, I plan to try the same tomorrow but with a regular V60. Thinking about it, I remembered that many multiple pours recipe warn not to let the beds go dry as this recipe does. So I am wondering, why not.

It'll drop the brew temp letting it fully draw down between pours. Could also contribute to filter clogging, not sure. But whatever works.

I wonder about slurry cooling more but wouldn't more oil sheen, strong aroma when I usually get little to no aroma, and deeper, richer sweetness be signs of higher extraction?

When I learned Kalita technique from Nick Cho many years ago, his technique included never allowing draw-down to expose the bed. I trust that he had tried letting the bed become exposed, especially as he was training his team for both commercial and competition. The reasoning may be a hypothesis, but it seems reasonable that a wet, exposed bed would cool quickly, especially with evaporative loss.

Nick was also really into zero turbulence with the Kalita, the pour was careful not to disturb the coffee bed to avoid any channeling. I went to a coffee talk with Nick and I believe someone from Kalita going into this and other theories of extraction. He also talked about hemicellulose taking about four minutes to break down and giving some additional sweetness. I posted some of the information from the talks on here at the time.

Would the immersion aspect of the Switch, for each pour until drawn down, guard against the channeling or other drawbacks?

I did same brew today but in plastic, non-switch V60. It was almost same but more floral-sweetness than direct sweetness I got in Switch and less aroma but had same oil sheen on top of coffee. Brew took 5:12 minutes versus 5:33 in switch, which was about same as I did bloom about 10 seconds longer but there were no 15 second pauses with switch closed after the 2nd and 3rd pours as I did in Switch. Also did swirls after each pour that I did not do in Switch. Bed stayed very flat.