The consensus here seems to always be leave in SDR and use match content, but I’ve had no issues with leaving Dolby Vision on all the time. SDR content like youtube and TV shows that were never mastered in HDR look 100% fine to me. Part of the Dolby Vision spec is that it forces your TV into it’s most color accurate settings so why wouldn’t I want that as well? Using an LG C2 by the way.
I would especially not leave the ATV set to DV or HDR if using an OLED TV. Forcing a higher peak brightness on content made not to go that bright and on screen savers which are supposed to help preserve your display will ultimately shorten the life of your display. OLED elements degrade with use and they degrade even faster with running them brighter. If you care about longevity of your OLED set then save the DV and HDR brightness for content that is meant to be seen that way.