Think about it like a "channel" rather than a lump of data. Audio is coming in through every audio "channel but it's coming from different sources. For audio tracks with clips, the clips are where the sound comes from. For audio tracks coming in from synths, the synth output is where the sound comes from.
Once the sound is into the channel, the channel works the same no matter what the source.
This is one of those things that's really obvious if you started out working on desks, and perhaps less obvious in DAWs. Probably because DAWs are largely programmed by people who started out working on desks, paradoxically enough.