Widgets can be resized to give your dashboard the layout you want.
To do so, use the cursor to grab the bottom right-hand border of the widget you wish to resize and drag it to the desired width and height.
Different sizes will give a widget different layout (i.e. the label on a number widget is moved to the right when the widget is longer than it is higher).
The number and text visualizations allow a height of half a grid. This is particularly handy for adding context to your dashboard or fitting two widgets instead of one for metrics that are less relevant.