Once upon a build...

Quick question, when building a game in Unity, does it include everything in your project folder, or just what you are using in your actual game? Does this differ per platform?

does it include everything in your project folder, or just what you are using in your actual game?

Neither. It includes everything that’s referenced in the inspector (so, essentially everything that you’re using), except: 1) scripts—all scripts are included whether they’re used or not, since there’s no good way to be completely sure as to what’s actually referenced, and 2) everything in the Resources folder, for the same reason.