Harmony is usually taught as a list of rules: which degrees go with which, which cadence resolves where. That works for passing an exam and less well for writing, because what decides whether a progression moves you isn't that it follows the rule — it's how the step from one chord to the next sounds.
Chord Cosmos reverses the order. The chords sit in a ring where those sharing notes — and therefore sounding natural in sequence — end up near each other. You place chords on the track, loop it, and decide by ear. You end up recognising why certain combinations work before you know what they're called.
Switching instrument isn't decoration: the same progression occupies a different region of the spectrum depending on what plays it, and that changes what room is left for everything else. A chord on piano fills the mids; the same chord on a pad spreads out and competes with the vocal. Switching while it loops is the fastest way to notice.
That relationship between timbre and available space governs an entire mix, and it's explained band by band — each zone playable — in the frequency ranges guide. As a reference to compare against by ear, there's the online piano.