This is a video series of 8 tutorials covering a variety of tips and tricks to use and leverage the masking features in ZBrush
Most of the techniques I covered in the tutorial series are very useful for high-poly meshes (specially when you are sculpting) and even though you could totally apply some of the workflows to mask low-poly meshes or hard surfaces models, there are other very handy tools that might be more useful in certain situations.
For instance, if you have a low-poly mesh with nicely distributed polygroups you can take advantage of the various masking features from the ZModeler. In the examples below, I took a cube with some polygroups and use the ZModeler to mask areas based on the 'features of the cube'.
With the ZModeler brush selected, you can press the spacebar over a face and select 'Mask' as your POLYGON ACTION and then use the 'Polygroup inner' in the TARGET to mask a specific polygroup:
Or the 'Flat Border' to mask just the border of a 'flat area of polygons' ignoring any polygroups:
Or the Polyrgorup all as TARGET which will mask an entire polygroup. This one is slightly different from 'Polygroup Inner' since the masks 'bleeds' towards the outside of the polygroups ensuring that 100% of the polygons marked with the unique ID are masked (in the example below the light blue polygroup).