I do this occasionally when riding, and more often on a spin bike. Massive climbs can either blow up your mind and body, or give you an opportunity to master both. Yogic breathing on long, steep climbs helps me stay in a sustainable power zone and keeps me from panicking (like I used to do on big hills), and maintain optimum heart rate.

I find it much more easy to apply this level of focus on a spin bike. It's like being in a laboratory. When I'm on a spin bike, in front of a mirror, I'm able to focus my effort, still my upper body, and optimize power. Do this enough in "the lab", and it transfers to the road.