Using the terrain composition nodes, there's only 2 decimal places in the edit boxes for translation/scale/rotation. Using the widget to move the terrain allows much more precision than that, so there's no way to know the actual translation used for the terrain if you touch the widget. Additionally, you can type values with better than 2 decimal places and your values are respected, but you can never see the precise value again.
Our use case is that sometimes someone will move this widget, then want to make another translation match it exactly. They would try to copy and paste the values, expecting them to line up - which they didn't do.