Looking at http://support.zortrax.com/printing-tips-m200/ the photos look very similar - what is the difference between shell and mesh?
Using Shell you can print model with 1-round wall:
Using Shell, your model wont get any top layers (if there are any) and you can 'get rid' of the bottom layer as well:
Mesh generates TOP and BOTTOM and on the surface it looks the same like any infill print:
Model above most likely collapse, due to lack of support/infill inside, but overall intention should be clear.
Last but not least, using Shell you can print in Spiral Mode, which more or less means printing without Seam: