A snubber is a good idea if the load is unknown, these drivers switch the triac on soon after zero crossing, so the load current will start from zero too ( although will go up quickly for some loads ) when the opto led drive is removed the triac will turn off as the load current goes through zero - as long as the re-applied dv/dt does not trigger it back on - some inductive or motor loads can provide a back emf which can trigger the triac back on - the snubber is to prevent this ... ( the dv/dt at turn off being too high )