Combining the best out of FK and IK spine rigs and adding even more. IK/FK spines are allow much control over the torso but are tedious to animate. A lot of layered controls on top of each other can require some counter rotating and produce gimble issues. With this setup the animator can rotate from various points on the spine. Similar to FK but FK requires the user to distribute the rotation across multiple controls if fluid shapes are required. And they always are.
On my setup most of the posing is handled with the rotation of the two main controls and can be further refined using the tangent controls and the translation of the main controls.
Advanced volume preservation controls plus the IK like behavior that can be achieved with this setup are great for stylized animations.
See it in action:
Tangent Spine Rig from Armin Halac on Vimeo.