When doing full-stack development, most times you'll be working with a front end client and some sort of API that the client will consume. For web development, this usually isn't a problem since your API runs on one port and the client is on another - everything can still talk.

Lately though, I've been getting into a bit more mobile development and was wondering why my Flutter app couldn't reach the API that was running on the same machine. Then it dawned on me that android was running in an emulator, so  trying to reach the API running on "localhost" wouldn't quite work.