the interval time just makes it start and stop welding over and over, so handy on thin thin metal, kinda like the pulling and letting go of the trigger thin metal technique, but you just hold the trigger in, also makes it look neater easier with evenly spaced ripples.
and the spot weld time can do one sided spot welding on thin metal, the thicker the wire the better imo, and the two sheets have to be held close together.