questions about p mechanism

[xcpky]

Say, I copy a line by xy
When I paste it, instead of pasting directly after the cursor, it opens a new line and pastes to the line after the cursor.
I think it's quite interesting and actually saves effort. But I don't get how it works.

[axdank]

if I am not mistaken, I think that when the copied line has the line break \n is the case that copies up or down in a new line, in the case that the copied does not have the \n at the end, paste without problems before or after in the position in which your cursor is.