Really interesting, makes sense.
It is an old salmon poachers trick. Nothing new here.
I've looked at discussion of this technique. From them and talking with people who have caught BIG fish i don't believe it's necessary.
I'm not a fan of this idea. I've landed some very big trout on a tenkara rod and 6x tippet without doing something that is in my opinion reckless and unnecessary. I know that Golden has also landed some very big trout without throwing a rod into the water to see what happens. I would rather break a fish off then leave it up to fate and see what happens, nope I'm holding on to my rod.
I would never do it (on purpose) because I value my rods too much and if the fish doesn't stop right away you could lose your rod or it could get caught on a rock and break, or the tippet could get caught on a rock and break and then your rod could float merrily away faster than you can follow.
I was at the same presentation that Morgan wrote about, and there's a little "behind the scenes" that may yield some insight. Throwing the rod in the water was indeed a tactic used by the British before reels were used, but I don't know how common it was or whether it was ever used on fast flowing rivers. Craig Mathews was told to do it by Yvon Chouinard, who introduced him to tenkara but who is also a bit of a provocateur. I can easily see him saying afterwards, "Yeah, I told you to do it but I never though you'd actually DO it."
Craig may be right about the fish not going far once the pressure is let off, though. One time after netting a fish of about 19" I threw my rod into the tall grass on the bank. I happened to be with a photographer, working on a DVD, and we did a number of "fish in the water, focus, quick lift and photo then back in the water" shots. I completely forgot that I had neglected to remove the hook. I let the fish go and we did a brief interview on the whole sequence leading up to the cast, the take, the fight - the whole bit. It was only then that I realized my rod was gone. The fish had headed downstream and took my rod with it. It turned out he only went about 20 feet and was behind the next good sized rock. It really was fairly easy to pick up my rod and land the fish a second time. Still, if there hadn't been a rock right there for him to duck in behind, who knows how far he would have gone.
It worked out that time, but I wouldn't do it on purpose.
I am pretty much on the same page as most other anglers here - I would also rather loose a fish than take a chance on loosing or damaging my rod. Side pressure applied in the opposite direction that the fish is heading will tire even a large fish pretty quickly. Another important factor is not applying too much pressure to the fish in the beginning if you can avoid doing it, and you usually can avoid too much pressure application by just relaxing the pressure on the fish after you are sure of your hook set. Most of the time, once the pressure is off, the fish will settle down surprisingly quickly. It is a common practice for salmon fishermen fishing out of small prams to hook a salmon and then relax the pressure on the fish completely, while the angler winds all the loose line lying in the bottom of the boat back onto his reel to play the fish off of the reel. Most salmon are considerate enough to wait for the angler to gain control of his line before the fight is enjoined again, when the angler puts pressure back on to the fish. The next time you hook a nice sized fish, relax the pressure and see for yourself what happens when the fish thinks he is free to go where he pleases.
I did that to a 20 lb flathead catfish once, but it was on a $5 bamboo pole on my pond (actually, I had no choice, the fish ran off so fast it took the rod out of my grasp). I don't think I would do that to a $120+ graphite rod that could get scrunched up against roots, rocks and/or driftwood in a flowing river. I'd rather the fish broke off and I had the pleasure of telling the story of the whopper that got away.
I watched a movie called "The River Why" where that technique is used by a few people to catch steelhead. Jim