The limitations on using any "on board" slave sensor is that it will typically have to be in line of sight with the triggering strobe.
This means that you will (a) see the strobe in the image and (b) you will get the harsh light that is output close to the strobe itself.
By using a remote sensor on a cable, it allows the strobe to be placed "out of shot" and the light to be directed/shielded in order to use the softer light that is further away from the strobe itself.
I used the Triggerfish with the YS-D1 and it was fine.
All the best