Looking at the documentation for tags, I stumbled across the predefined tag "EditorOnly". Does it hold any special attributes such as "MainCamera" does for the main camera? What is the intent of this tag?
Sometimes you may want to draw some waypoints or markers in the editor, to make it easier to debug your game. for instance if you want a patrolling guard to walk a route, you may want render the route in debug mode as a set of lines, and confirm the guard is walking along it, obviously you don't want these lines appearing in your game, so you can set them as EditorOnly.
I’ve made a test with Unity 2018.2.20f1 and game objects tagged with “EditorOnly” are being removed from compiled scenes. Prefabs remain however untouched and will contain game objects with this tag in the compiled game as well.
I would assume that the tag is supposed to be used for objects that should never appear in an exported game, like guide objects or the like. However, minimal testing makes it seem like no, it doesn't hold any special attributes. It's up to you to implement its purpose.