Selects portions of meshes and split them off as separate pieces
Subsetting a mesh allows you to delete or toggle invisible part of the mesh, or to shade the pieces independently, thereby increasing processing speed.
When this is checked, the new DAG nodes containing the subset mesh become invisible.
Choose ObjectDisplay > Visible to make them visible again.
When putting down points to select a region, this option specifies which triangles are selected when more than one side of the mesh lies under the selection polygon.
Visible Only – Only the front-facing triangles are selected. This is the default.
Include hidden – Both the front and back-facing triangles are selected.