I've just found that eventDestroyed() is called in the following scenarios:
* when you pick-up an oil barrel or artefact
* when you start construction of an oil derrick
In each case, the .player property of the feature object passed in to eventDestroyed() is set to the player who picked up the item or started building on it.
I'm using this to play audio messages, such as "power transferred" when a barrel is picked up, or "construction started" when a derrick is started.
I'm sure there are other uses for this too