This is just an example about Chillin.js, a layout engine on top of impress.js.
Chillin.js is based on impress.js.
And doesn't let you do more things, it just makes things easier.
You can see on impress.js' page for its neat demo.
Every slides you see until this one have been automatically positionned
But you've to write this complex positioning only when you need it...
Whenever you don't need anything, you just don't write it and focus on your content.
That's all.
Giving you a layout when you need it ...
... and some helpers for your positioning; letting you refer to any previous element.