The extra signal is key signature, it tells receiver different things on different keys. Yes, on the x-series of remotes the extra signal on menu key puts up different menu item depending on if the signal is on via- 963 + Ch UP, or OFF via- 963 + CH Down. This same signal is what initiates the message at the bottom of receiver screen if there isn't a tv code programmed to the tv device. Telling to program the tv device. It can also tell the receiver what brand of components are program to each device. This was way before receiver actually programmed the remote for you, back then in the menu there was a simple list of brands on each device. The user didn't tell the receiver what codes it used, the receiver recognized them by this extra signal.

This extra signal can also interfere with the actual IR commands making them unrecognizable to the components they were trying to control. Especially volume commands. It was more trouble , than useful. So turning off the signal, at least gives you sharper directv command, for learning remotes to learn.