As I was just looking for the folder holding Fallout Shelter save files, I noticed my user folder (%USERPROFILE%) contained a few folders named .AndroidStudio[insert number here]. More specifically, .AndroidStudio1.5, .AndroidStudio2.0, .AndroidStudio2.1 and .AndroidStudio2.2.
It’s sadly very common for uninstalled application to leave such folders behind, however they often empty it, and in almost all other cases at least such folders contain barely a few small files. However, in this case, those folders contained each 400MB to almost 3GB of data, for a total of around 4.5GB in 6000 files!!
So, next time you upgrade Android Studio to a new version, you know what to do: remove their previous data folder once you’re done migrating the old one.