In this society, we tend to think of softness as a negative. If being soft is collapse, laziness, inattentiveness, etc, then it would indeed be a hindrance to growth inner and outer.
We need to soften, though, in order to open or change. When baking a cake, we allow the shortening to soften so that we can cream it with the sweetener. When a seed germinates or a fledgling emerges, the shell softens so that the new life can burst forth.
When I soften as part of the first alignment principle, it is not a collapse, though it does have an aspect of easefulness. It is necessary to soften to invite the support of the subtle energies, to fully experience all the pose has to offer, to expand with light from the inside out. Softening when we start a pose is like the softness of early spring that allows the vigor of full growth to expand.
Being soft in this way — on or off the mat — makes possible the growth of inner brightness and strength that actually makes us less vulnerable then would creating or keeping a hard and brittle shell that can bind or break.