Gerry,
Earlier I also did not think the DTG is useful and later realised that it is implemented on most industrial controls.
And I've talked to a few guys who running industrial machines for living and about all of them used the DTG function when they setup the jobs on the machines.
It is especially useful when you send a movement via the MDI and the tool is near the workpiece or near a vise etc. and you moving towards it then you want to know how much the machine will move,
because you want to know if it will hit the vice or not. The guys who I talked with about the DTG all said that it is the most useful for this purpose.