The main advantage of this type of device is that you can use it to surprise your partner. The fact that he or she will not know when the vibrator will start working makes it exciting and adds mystery to your sex life.
The second benefit is related to introducing a third person into your relationship, which can be very exciting if both partners agree on this kind of experiment. Having someone else involved in intimate moments also allows couples to try new sexual practices that would not otherwise be possible with just two people alone together in bed!