I am usually tethered while on location. A larger screen allows you to notice fine details and provide quick rough edits when clients are nearby.
The 15" Retina display is truly gorgeous. Rather than downsample the resolution I choose to use the display at its true 2880 x 1800 native resolution which gives me great real estate and detail.
You get what you pay for. I am constantly helping friends with computer related issues and Macbooks just work reliably. I'm willing to pay 2x as much for a laptop that performs reliably 4x longer. Not to mention OS X is so brilliantly designed for power users and multi-tasking. That being said, Microsoft Windows 10 technical preview (very early look) also shows the addition of virtual desktops which has always been a huge selling point for Macs. Hope they pull it off well