One of the points. I see nothing wrong with 'the cautious' wanting to have RCD/RCBO protection of SWA (ideally, as you say, not sharing an RCD with other circuits) - it's certainly not impossible that damage could occur resulting in enough fault current to trip and RCD, but not enough to trip an OPD. In a TT installation, one obviously has no choice, but I would still want to use SWA for burying (rather than some other cable with an earthed outer 'sheath', if one could find a suitable one), if not only because of its mechanical properties.