You can take a chest with you mining, drop it, put your Diamonds safely within as soon as you mine them and empty your inventory without having to return all the way to your base.
It can be used to share items between multiple bases. You can store all the mine carts for your railway stations in the one chest and have them accessible from any station. You could have a public food chest, and everyone on the server could access it at the same time.
Each pad can be recoloured by using a dye on the pad or by using the following recipe with the three dyes in the crafting table.
If one chest is opened all chests with the same code will be opened.
As they are made of obsidian, Ender Chests are mined using a pickaxe (preferably diamond). You cannot change the code or break a chest that is currently open.