Rubble is the name given to the debris on the construction fields when starting the game or after a building has been destroyed or torn down. You can harvest it and gain some resources.
Here's what the rubble looks like in your village:
By hoovering green button, you can see:
which building was destroyed
the amount of available resources
time required for harvesting
By clicking the button, you start the collection. After the specified time, the resources are added to your stocks.
At the beginning of the game, you can simply collect the resources from the rubble. This gives you more flexibility while building your village up and speeds up the beginning of the game.
You also get a small amount of resources back when you demolish a building or when a building is destroyed.
More precisely, you get 1/3 resources back from demolishing buildings and 1/10 for levels destroyed by catapults.
This can help you when reconstructing buildings and restructuring your village/city.
Moreover, it helps identify which building was destroyed on this field, providing you a better city/village overview.
