Soundbar and TV are both LG and communicate/relay commands and power state via the optical link to eliminate the soundbar remote.
On the day of the install I could not find a 2nd HDMI Cable in my cable bin, so that I can run the HDMI via the Soundbar. Had the soundbar on Wireless Link for a while, but after a firmware upgrade the audio sounded tin-ish/hollow, so I decided to use the included optical cable and never had an issue since, even-though the sound issue was fixed with the next firmware update.
As a side note, I was shock to find out recently that the ARC function is not included as standard on all the newer model TVs, especially dumb TVs.