When I upgraded my iPad to iOS 10, I uninstalled many of Apple's useless apps: Maps, Mail, Calendar, Notes, Reminders, and so on. I use none of Apple's cloud services because I don't want to lock myself in to their walled garden. Some Apple apps, like Mail, do work with third-party services, like Gmail, but poorly. Mail is among the worst clients you can find for Gmail.
It's good to get rid of all this junk. I now feel my device is acting more in my best interests than in the platform maker's strategic ones. Is it my device, or is it Apple's? When I can get rid of bundled junk apps, I feel that it's more mine.
Making bundled apps uninstallable also makes me look at them more favorably: less as attempts to force second-rate apps on me, and more as suggestions from the company that I may find these apps useful, and if not, I can always uninstall them. That's a much more positive place to be .
Android is much better at this, letting you disable an app.
However, iOS 10 doesn't go far enough. On my iPad, I still can't uninstall FaceTime, Messages, Photo Booth and Find iPhone. Since the iPad doesn't receive SMSs, the Messages app is just a frontend for iMessage, which I couldn't care less for and which almost none of my friends use, anyway. Likewise for FaceTime. Find iPhone should be uninstallable because the user may not have another Apple device to find. And as for Photo Booth, I have no idea why an app that lets me apply silly photo effects to my face is a required part of an operating systems. iOS 11 should let me uninstall these crappy apps as well.
iOS should also let me set a third-party app as the default. Currently, if you uninstall Mail, and then click a mail link in a web page, you get a prompt saying there's no mail app installed. But there's one — Google Inbox. Just open it and let me send the email I wanted to. Apple is blocking the task I'm trying to do, and screwing up the user experience, out of a short-sighted desire to push their crappy app over a superior Google one, in this example.
Android again handles this better — it lets me set a third-party app as the default, though the intents UX is broken in many ways . Apple should copy Android and fix the UX.
In summary, it's great that iOS 10 lets me uninstall Apple's crappy apps. iOS 11 should go further and let me uninstall more unwanted apps, and let me set a third-party app as a default.
 It also reduces the chance of antitrust action, when a criticism can't be levied that a company is forcing its apps on users.
 You keep getting prompted for the same thing multiple times. If you choose to always open with a particular app, it's hard to figure out where to go to change that later if you want to. If you don't tick the "always open with" tickbox, you keep getting asked the same question umpteen times.
Often, I care more about seeing the content of where a link points more than which app shows me that information. Don't interrupt my workflow to ask me less important questions.
Some things generate prompts that shouldn't, like: Which app do you want to use to dial this number? Just use the phone app, dumbo! But this prompt sometimes inconsistently, one sometimes.
The intent UI sometimes appears unpredictably, like when I was asked which app to use when I pressed the home button. I didn't get asked that question earlier. Why then?
The intents UI is a complete failure.