Say you have a button of some sort and you want it to be in the lower corner of a dialog box. When closing in the size of the dialog box or when positioning the button near a corner or the box, show the measurements to the edges of the box it is near. Attached is an illustration.

(Currently, XD shows distance measurements only when the object you're dragging is snapped to the center or top/bottom/left/right of the other object -- not when it's close to the edge but not snapped).