The embellishment option in the mixer relates to the chord voicings being played.
OFF - the chord symbols are adhered to exactly. For example C^7 will contain C E G B
ON - the voicings may add other chord extensions for color. For example C^7 might add a D or A
For jazz, embellishment would normally be on; Pop off.
When exporting the midi file of a song, the embellishment setting is adhered to.