Well this is how I generally think of the little nubby horns (1-3 inches) that have the same colour as the skin (because the skin covers the growth from the skull)
As for why you'd want it. Because it evokes horns without fully having them. The skull is stretching out as if is wants to grow full horns but not so much that it actually breaks through the skin. Do the fiend has big horns, the half-fiend has small horns and the tiefling great-grandchild has these nubs that evoke their ancestor but are not like their ancestor...just enough to remind you that they are not quite human. Thus it also evokes that the dark nature exists under the skin as is waiting to burst out but is not open about it.
And also shouldn't those whose blood is touched by the dark forces be disturbing?