There are several specific advantages. Normal subs with an enclosure excite many room modes, due to their omnidirectional character. This leads to an uneven frequency response in a normal living room. Because of the directional nature of a dipole there are no standing waves to the ceiling and side walls. The bass of the dipole is deep because the resonance frequency of the woofer is not shifted upwards by an enclosure.
Energy is transmitted without the delay and the back-lash that is caused by a box.
It showed in practice that the quality is different from what most listeners anticipated as the sound of an open bass system. Also for me. The sub is precise, no matter if it has to generate pressure and attack for house music or to reveal the delicacy of a slap bass. Bass is very well damped, better than when a enclosure is used. The combination of the Quad ESL-63 and the sub woofer shows in symphonic works precise positioning and discrimination of instruments, and a great dynamic range while maintaining an impressive reproduction of sound stage and space.