Have you used one?
I've only had a quick dabble with one but I'm familiar with the displays. I believe the iPad 3 is a similar PPI.
For retina aware video/photo editing apps, you get all the benefits of a large res (more real estate to fit images/video in) without the downsides (having the UI look tiny).
Don't get me wrong I like pixels as much as the next person, but you're getting quickly diminishing returns on a screen this size. I just don't think it's worth it personally and have no problems photo or video editing on just "decent" resolution screens.
If it came as standard and didn't come with any caveats then fine, but the reviews suggest the GPU is flying by the seat of its pants at the highest resolution settings. I mean, seriously? One of the founding tenets of the Mac is hardware + software integration and yet they are charging a fortune for something that potentially struggles with its headline feature.
It's not for me, but for those who have one I'm sure they enjoy it.