Bayān miqdār ḥāl al-mushabbah is used when the basic quality is already known, but its degree, strength, weakness, or extent remains unclear. The comparison fixes that degree by pointing to a familiar model.
A listener may know that an object is black, yet not how intensely black it appears. Comparing it with a recognized dark object clarifies intensity.
The question is not merely “What kind of condition?” but, more precisely, “To what degree?”