When you're building a dashboard, you have an endless freeform canvas to place your widgets on. There aren't any restrictions on how many or few dashboard widgets you can have, and you can arrange them in any size or shape that you want.
Then, when you're done editing your dashboard and are viewing it full-screen, Dash will automatically shrink or grow everything so that it fits on the screen.
Dash's automatic dashboard sizing is probably best explained with an example. Here we're editing a dashboard and we've added two shape widgets, a circle and a square.
When we're done editing and showing this dashboard full-screen, Dash zooms the dashboard so that it fills the screen.
Let's go back to editing the dashboard. We'll add a pink triangle below and to the right of the blue square. Notice how the canvas automatically grows taller to accommodate the new widget.
Now when we view the dashboard full-screen, the circle and square are a little smaller because the overall dashboard is larger.
Let's go back to editing the dashboard one more time. We'll add a dog image below and to the right of the triangle. Notice that the canvas grows even taller and wider.
Here's what it looks like full-screen:
Again, for reference, here's what the dashboard looked like full-screen when it only had two widgets.
There are two side effects of automatic dashboard sizing that you should watch out for: