It was added a long time ago (I think during DOS1 or DOS1:EE times), indeed to make Osiris more OOP-like. That's also why some Osiris error messages talk about "the this object" when it's about parameter 1. It behaves exactly the same as when you pass that object as the first parameter.
That said, it did not really catch on inside Larian and we don't use it (any more). I'm not aware of any plans to remove it right now.
