Item repair

Item Repair allows players to repair damaged Tools or Items by combining them on a Crafting grid. Items can be placed anywhere on the crafting grid. The two weapons/tools you will be repairing must be of the same type and same material for it to work. The health of the item that is repaired depends on the amount of health left in the two used items.

One could argue that this is useless, and really only serves to save space rather than renew valuable items, as most tools are used one at a time, but it's NOT useless. For example: if you have two tools with ten uses left, combine these to make a new tool that will have 25 uses left. Notch confirmed this mechanism on his twitter.