I use it to quickly sketch out different progressions and try out various chord substitutions and alternatives. Once that’s settled I write out a real part with a midi editor. Additionally if you set the colors in the Key Editor to the Chord Track and are writing a melody for example it is visually easy to see which notes are in or out of the chord or scale.
Also I find it very useful as documentation. I used to use the notepad to write down my progressions, but now I use the chord track which is better since it aligns with the actual music. I’ve recently looked at some songs I wrote 20+ years ago on guitar where I only seemed to write down the lyrics and not the chords (apparently I thought I’d never forget, wrong, wrong, wrong) - over time I’ve come to appreciate the value of documentation. 