# Split (shortcut y) face to limit loop cut?

I was trying to vertically-cut only one face like the screenshot blow. I remembered that I saw a man of a fairly large Blender channel on YouTube using split (y) for that. Basically, he was creating a window on one side of the wall of a room by adding two lines vertically and two lines horizontally using loop cuts. But before he was using loop cut, he selected the wall (one face) and pressed y.

I created a plane and then added two horizontal loop cuts. Now I had 8 vertices. But when I selected the middle face and pressed y, the number of vertices became 12. Does this mean that there are duplicate vertices on the same places? I searched Google for a way to limit the loop cut and people were suggesting "subdivide". So, I created the same shape as the screenshot below by both 'y' + loop cut, and subdivision. The former resulted in 18 vertices, the latter resulted in 14 vertices.

So, in short, was it a good idea to use "split" (y) as the YouTube presenter to limit the loop cut to one face?