What precise purpose do pets serve in their 'normal' capacities, if not 'emotional support'? I'm not necessarily saying such a thing is beyond the pale as a su

What precise purpose do pets serve in their 'normal' capacities, if not 'emotional support'? I'm not necessarily saying such a thing is beyond the pale as a support animal, but that this use is contiguous enough with "pets" as to draw into question the validity of a threshold.