Can I pass on a good IPS monitor if I get Retina MBP

I have scoured the net to answer this simple question but could not find many opinions.

Can I go without a good IPS monitor (say Dell U2413M) if I get the retina MBP?

I am not a professional photographer and am taking pictures for fun - mostly of my kids, some nature, some sports etc. Picked up photography a couple of years ago and started using RAW a year ago. I have been using early 2011 MBP and LR 3. The TFT display is not good, that I know from experience.

How have you found the retina MBP for correct color/contrast editing? Do you get enough real estate? Is it enough or do I really need a standalone monitor? I would like to be able to take the laptop and sit on the couch (the light is controlled) while editing the photos or edit the pics while still on vacation.