The main reason for using this is to refference the common IC regulator pin-outs which we use all the time and for the same reason when using Op-AMPS. OP-AMPS almost always use a common pin-out depending on their cinfiguration. IE: Single, Dual and Quad packages. However there are a few anomalies. There are also show the pin-outs for devices such as the LM13600 OTA and NE571 compandor chip along with a few sundry logic devices.