They can be surprisingly useful, but not in the way you would intuitively expect. Herewith is another technical post, so feel free to skip it if you're not interested in content creation for latter versions of DAZ Studio.
What rigidity actually does is affect the degree to which generated FBMs affect a clothing mesh. The DAZ documentation is here: http://docs.daz3d.com/doku.php/public/software/dazstudio/4/userguide/creating_content/rigging/tutorials/rigidity/start
I find this a bit puzzling inasmuch as what it suggests rigidity be used for - the center ring on a bikini, buttons, buckles, clasps - is exactly what I've found it hardest to get good results with using the feature.
The issue is that for smooth and continuous deformation, the rigidity group needs a good set of reference faces around it, and it seems to need them to be continuous with the "rigid" verts. So something fully discontinuous, like a discreet submesh (as most buttons and buckles must be) is going t