What does Xcode do well? Xcode is a great tool for when you want to do Apple device development. Xcode worked for me when I had to do native iOS development (there are certain things in apps that can only be done in XCode using Apple's own methods). However, when your app doesn't require the very fine-tuning of some native apps, then using Xcode is overkill and is more effort than is necessary (it's better to use something like React Native or Ionic or Xamrin).
What does Xcode not do well? If you're not doing Apple development, then Xcode is not a good fit.
What do you wish you had known about Xcode before using? If you want to do native development, then you don't necessarily need to use Xcode. There are other great options like React Native that can do almost as precise of work as native code.