ToGo, as has been said above , displays the distance left to go on the commanded move.
For example if you are at x0 y0 and you have NOT pressed the ToGo button, if you command a move to X10 Y10 then you will see the X and Y DRO count up to 10 as they approach the target location.
If however you have the ToGo button pressed then the DROs will start at 10 and count down to 0 as they move towards the commanded position, in other words they are showing the distance left to go as they aproach the commanded position.
Hood