The spine is the power of the scissors. All styling scissor blades have a slight bend inward towards the opposite blade (called the set of the blade). This converging force at the point where the blades meet causes the hair to be cut. The stiffness of the spine is the force that makes this happen. The spine needs thickness and bulk to be stiff enough to provide the force necessary to cut the hair. The spine of both blades should be very similar, so one blade does not overpower the other one. This also applies to thinners. While the cutting blade does not have to be as wide as the tooth blade, the spine needs to be of similar thickness and bulk.
Hikari says the same thing about their new Dragon scissors: “Most scissors taper as they get closer to the tips The Dragon maintains its thickness and weight all the way to the tips. This new geometric weight balanced blade design provides excellent power and leverage when cutting wet or dry hair. This results in a powerful scissor with less overall weight and bulk.”