For ME, I prefer to set the sub power to ON. With the subs powered on during a movie. There should be less of a delay when the LFE audio signal is sent to the subwoofers. You should experience the full LFE signal event. With auto there may potentially be a delay with the subwoofers responding to the LFE signal. As subs would need to turn on (wake from sleep mode.)
You may find this helpful.
I don’t prefer to leave the subs on all the time 24/7. I use these RF controlled plug in outlets to remotely turn the subs on before enjoying a movie or concert and off when I am done enjoying a movie or concert.
I use a RF controlled plug in outlet. Plug each sub into a RF controlled outlet then plug the outlet into a wall outlet. Now when I am done enjoying a movie or concert. I turn the subs on/off with the RF controlled outlet.
Twin Pioneer AVR Locomotives-Elite SC 97, SC 1222 7.2.4, DOLBY Atmos and DTS X, (Front Pre Out,) JBL Pro Synthesis LS Series Speakers, F L R-LS80, Cen-LS, S L R-LS60, SB L R-LS60, 4 Dolby Atmos Enabled Klipsch R41SA, Twin Klipsch R120SW, Sony XBR 85X 850G, Sony UBP-X800M2, ATV G4, Yamaha ATS 1060 Sound Bar, True Depth Firestorm 2.0 3D Glasses, Harmony Hub with Utlimate 1 Remote, Broadlink RM Pro2, EYE Pad Air, Winegard FL6550A