Getting ARC to work can be tricky sometimes. There is another standard, CEC, which allows devices to communicate with each other for power and input control. For example, turning on your satellite or cable box and having it automatically power on your TV and AVR. This works through the HDMI connection.
The problem is that manufacturers use different implementations of CEC and they are not all compatible, so CEC has become a crap shoot as to whether it will work or not. On my system, the cable box will power on the TV and AVR but it will not power them off (the TV stays on). If I turn on my streamer, CEC should make the AVR switch to the streamer input, but it does not. I need to switch manually.
A lot of members here just leave CEC off because it can lead to strange behaviour. On my Samsung TV, the manual says I have to have CEC enabled for ARC to work. My cable box needs CEC to be enabled to automatically detect the best surround audio mode. So it depends on your equipment. If you use the built in streaming apps on the TV, using the optical out on the TV is the most likely to work trouble free, but the optical cable only supports certain surround modes. If ARC and CEC work correctly, that is one less cable to the TV (you eliminate the optical cable). This only applies if you have devices connected to the TV or use the built in apps. If all sources are connected to the AVR then it's not a concern.
