For example, when resizing, it will display the new dimensions of the resized object.  Here's a button being resized in a LinearLayout; in the horizontal dimension the width is being set to 176dp, and the height is being set to layout weight 0.31:

As another example, when drag & dropping in a RelativeLayout, during the drag the proposed constraints are displayed:

The tooltip positions itself such that it does not obscure the constraint feedback.