Brevity matters because some circumstances do not permit leisurely explanation. The commentary refers to ḍīq al-maqām (a constrained setting) and farṭ al-saʾāmah (excessive weariness).
In a quick announcement, «إِمَامُ الْمَسْجِدِ حَاضِرٌ» (“the mosque's imam is present”) identifies the person efficiently through a familiar relation. In an argument where the relation itself is contested, a longer explanation may be better.
Thus verbal economy can be an advantage but is not an absolute command to minimize words. Appropriateness to the audience and situation remains the governing standard.