The user should be given the ability to assign a mixer's track output to go nowhere. This is because, if the track is used as the source for a sidechain, you want to be able to keep the sends on post fader. This saves you an extra mouse click the pre/post fader button. But, more importantly, it would also mean that you can control the volume of the sidechain signal using just the one main mixer fader, globally for the song, and without wasting another plugin. It's actually a big savings for a small addition.