Unity added Assembly Definition files in Unity 2017.3 these were handy for packaging up code. In Unity 2018.1 they now work the way you would expect. Helping improve compile times, but they can still be tricky to hook up with Editor folders.
Unity PropertyDrawers are incredibly useful they allow you to separate editor Ui extensions into reusable code. If you aren’t using property drawers or editor scripts you are missing out on a major benefit of Unity.
In Unity you will find yourself wanting to do some process before you build a game, whether it be Asset Bundles, moving platform specific assets to Streaming Assets or just ensuring the build version information is up to date.