The prism layer settings at the interface level allows you to decide whether prism layers are grown from the interface or not during the volume mesh generation process. Certain applications such as those that include a porous or a rotating region do not require prism layers at the interface while others, such as fluid/solid regions require a prism layer on one or both sides of the interface.
The option to activate them or not is provided via the Interface Prism Layer Option node, located within each interface node that exists. The default state for the Grow Prisms from Interface option is off. This option is shown below:
Custom prism values specified for a boundary belonging to an interface are only included when the Grow Prisms from Interface option has been enabled.