...and you get all of that real estate when looking at images, video, and countless other things that love having pixels all without having to change any settings (default retina mode).
Also in the default retina mode you get UI elements and text at normal sizes so you can actually see them and work with them again all while getting full access to all of the pixels for content that truly can use those pixels.
You can also adjust the scale if you want using the standard displays system control panel (not just up to 1:1) giving you more physical space by shrinking UI elements but you lose the fidelity gains of course and will have a harder time interacting with them.
Folks should play with the interactive image under the retina section on the following page if you don't fully get what is going on with this display. (of course real life use of it is the best to get a sense of what it is like)
http://www.apple.com/macbook-pro/features/