I think it only makes sense for rehab or renovation in a house that has a pre AFCI style panel that you don't want to replace. (Zinsco or something)
I am surprised these are not dead front. If you are just putting in a few circuits that need to be AFCI, this makes a lot of sense. I imagine you could get 2 in a deep 4x4 or 4 11/16 box. That might be enough for a small addition or a basement remodel.
Prior to this you were running a feeder to a new style sub panel that you could buy AFCI breakers for.
