[Snappy Phoenix]

Other than not having apps refresh automatically which I actually prefer, I only want them to refresh when I open them anyway, what am I missing if I keep my iPhone 6S in low power mode all the time?

Also, my phone was in low power mode and the battery was around 50% when I set it to low power mode, so when I connected it to the charger, after a while it said now exiting low power mode since I have adequate charge or something, does that mean it would go back to low power mode automatically later or I would need to manually set it to low power mode?

[SnapThrow]

"Downside" is a subjective opinion based solely on your specific needs/wants from your iPhone. According to Apple, Low Power Mode:

"... reduces display brightness, optimizes device performance, and minimizes system animations. Apps including Mail will not download content in the background, and features like AirDrop, iCloud sync, and Continuity will be disabled. You can still use key functions like making and receiving phone calls, email, and messages, accessing the Internet, and more. And when your phone charges up again, Low Power Mode automatically switches off."

So if this reduced functionality works for you then not much of a downside for you...

[nnahorski]

Also, my phone was in low power mode and the battery was around 50% when I set it to low power mode, so when I connected it to the charger, after a while it said now exiting low power mode since I have adequate charge or something, does that mean it would go back to low power mode automatically later or I would need to manually set it to low power mode?

You have to turn it back on manually. I believe the iPhone stays in low power mode until the battery is charged to 80%, and then it turns off automatically. You won't be prompted to turn the low power mode back on until you reach 20% again, or you can flip it on yourself whenever you want.

[Ledsteplin]

Auto lock would be set at 30 seconds on low power. This would be a huge downside for me.

[Not Quite Right]

My question would be, why even buy a smart device if crippling it's functionality was your goal? Leave the thing fully functional, plug it in from time to time, and life goes on ...

[Shawn Schrader]

use mine in low power mode alot when im using it heavy. 6s doesnt have a huge battery so when using it heavy i switch on low power mode.