I feel sure there are physiological benefits from breathing techniques (and I naturally adopted the nose/mouth pattern while hiking the Rockies).  In fact, I started to develop these techniques 50 years ago while playing varsity sports, specifically basketball.  I was gauged as the most "fit" person on the team and anytime the team went to the "box and 1" zone, I got to be the chaser.  

The earliest acknowledgement of the fact that I was doing something different came from by team mates when they hung the nick name "smiley" on me.  I achieved this moniker because soon after wind sprint drills began, I started smiling.  (I can only guess that opposing team members thought of this behavior, but I'm guessing they were depressed by it.)  In any case, what I found by experience is that when I smiled (which also takes less energy than frowning) that facial configuration tended to significantly open the airway.

During games, I refused to take a seat during time-outs because I wanted to be able to fully extend my diaphragm and thus recover more quickly.  (I also suspect that lactic acid buildup in your leg muscles is diminished more quickly with the better circulation standing is likely to afford.)

However, all of this being said, I also think there is a probable psychological component to some of this.  While executing a specific breathing pattern, it is likely that at least some of your mental attention is drawn from your level of fatigue and focused on your breathing.  One personal benefit of knowing this is that when hill climbing, I'll take a quick look up to confirm the trail direction.  However, there after I never look more than 20 feet ahead.  Its amazing that I'll reach the top much less fatigued than if I watch my progress up the hill the entire journey.  To some degree, portaging a canoe up hill produces this result since you'd likely need to at least tilt the canoe upward to see the top of the hill.

Anyone else have a similar experience?

dd