I would like to suggest that proper posture and movements are a good way of researching how to deal with hidden dangers!
There is a common mistake to see aikido as a fighting art. It is an art based on the first reaction and a dodging skill is essential. I think, that the idea of relaxation is fine, but definitely in dojo. In daily life it depends on our assimilation to an environment and our preparation to deal with obstacles. For example, it is visible who is prepared to take an exam (any), and who is not. Our brain decides how to choose a self-defense reaction. Any extra breathing, a posture, actually do not help.
We just got used to see Master Morihei Ueshiba as a person with a magical power, instead to see him as a skilful practitioner of Martial Art. He was a good swordsman but he never suggested to focus on weapon in aikido training. However he became famous because of "the ship accident". It took place on a navy ship where Ueshiba has been challenged by a naval officer who had a wooden sword. He couldn't strike Ueshiba at all (not a single strike). Ueshiba kept dodging his attacks and thrusts until the officer fell from exhaustion. That is a clear example of what aikido is about.