@GazzaGarratt It is the most efficient way to mine in Minecraft, the simplest way to explain it is with this picture, with white being tunnels and grey being rock: https://goo.gl/images/y2l6rk You can therefore see at least one side of every block without having to mine every block.
Generally though, stuff is grouped together so your tunnels can be 3 or 4 blocks apart and still have a good chance of finding stuff. You can read a lot more here: https://minecraft.gamepedia.com/Tutorials/Mining
I generally stick to branch mining simply as I find it the easiest to navigate but others may find a different method best.