Using iOS8 and later devices with Xcode?
One of the reasons why software no longer installs, such as you can't install Sierra or Xcode 9 has more to do with Apple making your computer obsolete.
Here is a recent (2016 Addition to machines no longer supported by Apple), and there are so surprises there.
I have a perfectly running iMac Early 2008, and 2 years ago it was placed on the obsolete list. I can no longer update certain programs, such as install Sierra or Xcode 9.2.
There are some very disgruntled people who purchased MacBooks and Apple made them obsolete without even introducing an upgraded machine to replace it.
Now, if I want to have my Apps run on the new iOS 11 OS, I need to replace a perfectly good and working machine. That is not right.