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.