One reason for discrete "on" and "off" codes is for use with macros. For example, you might want to create a "play DVD movie" macro. Well, the first step in a macro like this is to power on all necessary devices. However, if you are already watching TV and then hit the button for that macro, a toggle "on/off" power command would turn everything on (if not already on) but the TV, which would be switched off. On the other hand, if a discrete "on" power signal is sent to a TV which is already on, then nothing happens. This way the macro will be effective whether the TV is on or off.