You can remove unaffected points from a deformer set based on which points the deformer is affecting. Use this to avoid unnecessary calculations for points that are not being affected by the deformation. Prune Membership is available for only Cluster, Lattice, Sculpt, and Wire deformers.
The pruning operation considers only the current position of each component in the undeformed and deformed versions of the geometry affected by the specified deformation. If you have animated attributes of your deformation, the pruning operation is performed based only on the current attribute values. This means that components that are potentially affected at other frames of your animation might get pruned out if they are unaffected at the current frame.
Since a typical blend shape operation has weights of 0.0 for some target shapes at any point in time, this operation is especially dangerous when applied to blend shape deformations. For this reason, there is no menu item provided to prune membership for blend shape deformers. However, you can access prune membership for blend shape deformers through the command line.