Definitely not saying it was useless, just that the utility was limited because of the usual limitations of MDA; that is, it's definitely not the same as what people would think of as a dual-head setup today.
That said, I literally was born after Windows 3.0. So... I never personally dealt with such a setup. Maybe some day, as a matter of exploring older computers, I will get a chance to actually run such a setup and see what it was like.