while @mijostyn 's points are salient to any subwoofer discussion, in my view and experience they are not practical obstacles to having subs (at least rel subs in my personal experience, but i know there are other excellent subs out there) work in a totally satisfactory manner for very high end systems for very discriminating listeners
i would also add that sub bass infomation is also very much about helping the system develop a very palpable sense of space and natural propogation of transient information approximating a real life listening or performance venue