On a Retina MacBook Pro 15-inch, the screen is actually 2880 X 1800. For some tasks, using full resolution is handy, try out Pupil for free to see if it suits your needs.
At full Retina resolution, fonts are tiny, which might be fine if you have 20/20 vision and are relatively young. But otherwise it gets old fast.
Still, for some uses (graphics mainly), forcing the screen to native resolution can be handy.
Retina grade images
You don’t need to mess with the screen resolution to enjoy Retina resolution. Some applications support it natively now (Photoshop and Lightroom). But it is the rare web site that offers anything suitable for retina displays.
Click the image below to see just how big a Retina display can be in native mode.