Yes, you need to use either arc or optical to send audio from the tv to the receiver. If you watch tv without the receiver (using the TV's speakers instead), then it's optional. But you probably want to do it anyways in case you want to watch tv and have the audio sent to the receiver for the times you want surround sound.
Note I said arc or optical as either is sufficient for the audio formats you'll see with OTA tv (namely Dolby digital). EARC is necessary only if you want the HD codecs you might find with Blu-Ray or UHD Blu-Ray and somehow don't want to connect your player through the receiver and connect it via the tv instead.
Basically the optical port or arc/eARC is to send audio from the tv to the receiver - which can happen if you use the TV's tuner or apps that generate sound within the tv. Or if you connect HDMI devices direct to the tv, which sends audio to the tv. That audio will need to use arc/eARC/optical to get sent from the tv to the receiver.
However, if you use HDMI from the source to the receiver then to the tv, the receiver gets the audio from the source directly and arc/eARC/optical is not needed.