The auxiliary pin is an auxiliary object designed primarily to end unconnected wires. It does not represent any electronic component (not even conductivity). Therefore, auxiliary pins are not included in a bill of materials report.
Auxiliary pins can be used as provisional points for connecting wires, so wires can then be placed even before placing connectors, terminals, etc. The wires of an auxiliary pin can later be reconnected to real pins using the Reconnect command.
It is also possible to create "virtual" auxiliary pins within grouped pins, including ribbon grouped pins and special components (see Connections for details). They may then serve, e.g., for connecting "spare" wires in a cable; note that unconnected wires cause warnings in the Tasks list, while those connected to auxiliary pins do not!