A friend has a 16gb iPhone and has managed to deal with that little space until just recently. She'd run out of space completely, I'd hand-update apps one-at-a-time trying to free up temp download space. Deleted her local music. A few weeks later deleted her local photos. iMessage claimed 1gb of space, it's a little opaque and manual to clean delete things. I finally convinced her to delete all messages older than 1 year. She got 500mb back. The next day her phone was full again without an obvious reason. Backed up her phone and restored. Everything seems to be there and now she has 5+gb free.
I was having the battery issue they're fixing the 6s for. Because I knew they'd ask I restored my phone (and grabbed yesterdays update because that had a fix related to this, too). It seems to be fixed as well by restoring.
...but all of this is souring me on Apple. I wish I was more confident about other options.
https://www.cnet.com/how-to/out-of-space-on-your-iphone-try-...
However, in my case had I tried this and it didn't work.
3 was allegedly fixed in iOS 10.2, which just came out.
1) Unlock process: When the fingerprint reader fails it now takes several presses on the home key to get a keypad to pop up so I can input my code. With previous versions I could just swipe when I knew the fingerprint reader would fail (e.g. wet hands).
2) App updates: When apps are updating on my phone it decides it really wants to stay on the home screen. I can swipe to get to the other screens, but it goes back before I can tap any apps. Also, when I can get into an app they tend to lag and crash more when updates are happening in the background.
3) Control Center (bottom menu): Trying to slide the brightness or volume controls on the control center menus usually gets interpreted as a swipe to the next control menu. I have to be very precise when touching them for the sliders to actually work.
4) Safari: Auto-hide of the control buttons does help page visibility, but showing them seems to be glitchy as hell. They appear and then disappear before I can move my finger to tap them.
5) Crashes: At least daily now the whole phone crashes to a black screen and then comes back to the lock screen a few seconds later. Seems to involve location services.
Also, not exactly iOS 10, but the new Watch OS completely broke the usability of the Weather app for me. Something that was fairly intuitive and useful is now cumbersome and basically useless to me.