The distinction makes it possible to talk about the featureless without resorting to pure maths.
Many languages have nouns, verbs, adjectives, &c. How would we apply any of these to a no-thing; featureless, changeless, timeless? Attaching gunas makes it possible to conceive of and talk about Brahman, though with features it might be proper to call it by a different name.
The material world around us is dualistic, it's full of different things, and it's layered, ie: hierarchical. The 'things' are made of parts and substances. These are made of molecules, which are made of atoms -- and we're already down to only 92 'things' in the world. But atoms, too can be subdivided, as can component baryons like neutrons or protons, "composed of" of various flavors of quarks. A proton, for example, has two up and one down quark, but this accounts for only about 1% of the proton's mass, the rest is in various binding energies, -- its Shakti -- and so on.
This doesn't mean there are two types of Brahman, or that the distinction is unnecessary. Brahman is a concept of theoretical physics; a metaphysics articulated as best a primitive people could, with the inadequate linguistic tools they had.
Physics seeks a single, fundamental, unifying "stuff," "force," brane" or "brahman," underlying all reality -- from which reality emanates.
There are not 'two types' of reality, and perhaps these 'distinctions' are irrelevant to the average householder, but this does not make them meaningless to philosophers, sadhus or scientists.