You can create a family that is hosted by the active work plane. This can be very useful both in a project environment and within a nested family where you may need a nested sub-component to reside on a particular plane. You can make any non-hosted family a work plane-based family.
In the nested family below, the rectangular extrusion is a work plane-based component. On the left, the extrusion is work plane-based but not always vertical. On the right, the same extrusion was reloaded into the family after designating it work plane-based and always vertical.