Which obscure iPhone setting genuinely improved how you use your phone, and what does it change?

I’m not looking for gestures or the usual tips that appear in every list. I mean an actual option buried somewhere in Settings that solved a real annoyance, improved privacy or accessibility, changed how an app behaves, or made your iPhone noticeably easier to use. Please include the exact path to the setting, what it changes, and any downside you noticed. Some settings sound useful but also disable another feature, use more storage, affect notifications, or change how the phone behaves elsewhere. What is the one setting you would immediately change again if you had to set up a new iPhone from scratch?