Unity allows you to directly add Blender files in Unity. Even though this is not recommended practice, some teams still prefer it. For these teams, temporary blender files should be ignored.
There is really no reason to not include these by default. If you don't use FMOD, no harm done. But I've seen many teams fail to add this to their gitignore and getting unnecessary git conflicts that could have been easily avoided if this were in from the beginning.
Idea is used by JetBrains (as to my understanding) and, as to my understanding, may in certain setups create cache directories. That's no good, these should be ignored.
Since a long time, developers have been able to use Visual Studio Code inside of Unity. I don't claim exactly to know how it works, but regardless its cache directory should be ignored, whether it is ever created or not (if not now, it might be in the future).
Casey Hofland