We do a lot of our work on a pair of identical high-end late 2011 matte-screen 15" MBPs (we went with last ones you could DIY upgrade). Screens are very good, more than 16GB would be nice with larger files, but isn't end of world. Biggest draw to a larger monitor is screen real estate. When using just laptop, the need to have to shift PS tool palettes around while editing and not so ideal ergos of a laptop (vene on stand) does make a larger monitor very appealing.
Keep thinking of adding say a 27" 5K iMac, etc, but fact that MBPs work really well, are bulletproof, we can swap for another if one dies, either are can used for tethering, both have FW and TB (that said USB3 would be nice for cheaper drives) and we can swap-out any drives/SSDs at will is very appealing...
In short, one can easily work from just a good laptop, but a nice larger screen has strong merit.