>> "
Apple took a lot of flak for not having multitasking, but to they credit they took the time to build explicit APIs that allowed apps to handoff certain whitelisted tasks"
iOS's support for background tasks is still shit. This is why some apps have been abusing the location API to ensure that background tasks don't get killed. Apple deserved all the flak it got and it still does.
_Example 1:_ fetch email (without push) for any non-Apple email app will not work reliably, because the app can get killed. You have to rely on Apple's built-in notification support, but this means that a server-side connection needs to be maintained.
As a result, if you want reliable mail delivery without using Apple's Mail, you have no way but to share your username and password with third-party app servers which you don't trust. For example: Airmail or Canary Mail.
Of course, Apple's own Mail has no such restrictions because it is a special part of the OS. This is no surprise however, since Apple has been actively hostile to alternatives for their own apps.
_Example 2:_ backing up photos and videos (with Dropbox, Google Drive, etc).
There's no way to ensure that your photos get backed up without making an effort to keep the app active, in the foreground, with the screen on, or without the app developer abusing the location API, which Dropbox has been doing.