"Optional commentary" refers to commentary or remarks that are not required or necessary. It means that the person has the choice to provide additional thoughts or comments, but it is not mandatory. Full definition
Lastly, there are five deleted scenes included with optional commentary tracks available from the director. (mediamikes.com)
Each short is accompanied by a lovely original score and almost half of them feature optional commentary by a comedy historian. (parallax-view.org)
It also comes with 12 minutes of deleted scenes and 5 more minutes of alternate scenes, both with optional commentary tracks. (combustiblecelluloid.com)