It's the inductive spike from the relay coils that you're isolating from. I'll agree that the inductive spike is usually not a problem (as long as the module is properly designed with a flyback diode -- and it is); I'm just trying to set the record straight. OP never provided any detail about his project that would let us know if the optical isolation was appropriate or not.
The "VCC" pin on the relay module is only providing current to the LED side of the optocouplers. The "JD-VCC" pin is providing current to the transistor, optocoupler phototransistor, and the relay coils. There is appropriate isolation in that respect.