After chatting with Google - online chat. I was told to leave HDR+ on most if the time to play it safe. You'll notice if you turn HDR off completely things look a little to light and fuzzy indoors, and with HDR+ Enhanced on all the time it looks to dark. Me personally I keep HDR+ on all the time except for night shots and landscapes. They said you don't have to do to much thinking because it has a form of artificial intelligence built into the camera so even with HDR+ on in the wrong situation it turns it off. 99% of the time it will think for you, kind of like Bixby or Google Assistant. It's way ahead of its time. Even with The Pixel 4 coming out in 2 weeks. The Google pixel 3a XL's camera still ranks #1 today!