The distinction is clear and relevant because the mass distribution is strongly bimodal. A stellar black hole is the result of the gravitational collapse of a single star (well, or two at most). And maybe some of them have since then merged with a companion body. There are zillions of these in any given galaxy. Whereas there are maybe one or two supermassive black holes per galaxy, sitting in the center, with mass of millions or billions of suns, and we don’t quite know how they first formed and how they have accumulated so much mass. If the difference between "one" and "billion" doesn’t matter to you, well, ok then.

The difference is even more clear-cut because so-called intermediate mass black holes are something of a question mark. For a long time it wasn’t clear whether they even exist in any significant numbers, and even now the evidence is not especially rock-solid, especially with regard to candidate objects in the Milky Way.