The purpose is to hide the evidence so it can never be found.
It happens often in murder cases. Generally speaking, they like to keep an eye on where the body is to ensure it isn't found. This is a reason most bodies are buried in the vicinity of a perpetrators home or an area known very well to them. Many murderers will periodically drive by where their victim is buried to ensure they are 'safely hidden'. Many remove the body at a later date and bury it somewhere closer, and in particular, under concrete.