The breed standard for a Australian Cattle Dog (Heeler) is to leave the tail. Most breeders no longer dock tails. A true working dog needs his tail for balance.
In my area docking is still popular. I own 4 Heelers and 3 are docked, were already docked when I bought them.
Docking after only afew days old would be surgery and require the animal to be put under. More painful and longer recovery time. Why put him through it?
My "tailed" dog has never knocked anything over with his tail and he's in the house.