The Deformation nodes category includes all the nodes which are used to make deformers. In Harmony, deformers are made of chains of deformation nodes connected in a hierarchy. By default, deformation chains made with the Rigging tool are created in groups by default to avoid cluttering the Node and Timeline views. Each deformation node represents a point in a deformation chain.
This category also includes nodes that are made to deform drawings without being part of a deformation chain, such as the Mesh Warp node.