For me the first thing I'd want is default apps. Safari, Maps, Podcasts are all things I would prefer not to use if it wasn't the only option to open in many many different scenarios. To get their alternatives I have to go select the app manually, can't call it from within another app and pass it data.
The second thing is different power profiles depending on charging status or location. If I'm out and about, I want my screen going in to low power after 30 seconds and off after 60. When I'm at home sitting on the couch watching TV, I want twitter/FB/slack/discord/whatever to open and stay open and my phone not to lock. I got an iPad specifically so I could have these different settings and a larger screen, but still get annoyed by it when I'm not home but on charge (thus without the iPad).