To add to a sibling comment, the distinction is important, because observed mass of black holes falls largely into super massive (millions to billions solar masses) to stellar (dozens of solar masses). There is very, very, astonishingly few observed black holes with an intermediate mass. So, how super massive black holes form is a mystery, and finding large stellar mass black holes starts filling in (possibly) that evolutionary gap in black holes. Not a physicist, just read/watch a lot of pop astronomy/cosmology.
Also, super massive blackholes can only "swallow" so much matter at a time. Given what we know about how fast a black hole can grow, super massive black holes seem to be bigger than should be possible.
