Why do i need BaseEngine.ini->EditorEngine option, if i have already UnrealEdEngine option?

We have:

[/Script/Engine.Engine]
EditorEngine=/Script/UnrealEd.EditorEngine
UnrealEdEngine=/Script/YourGame.YourCustomEditorEngineClass

I dont understand, why we need config “EditorEngine=”, because it is only base class for UnrealEdEngine and should not be used as standalone…