Why do you need line spacing?

Answer 1

In order for lines of text to be read, they cannot all be written on top of each other, so they need to be spaced out. Line spacing determines how much space is between each line of text. The standard is for each line to be immediately below the previous one, as you would see in this answer. Sometimes you want more spacing. This could be to make things easier to read, or because there is not a long of text on a page and it looks better if it takes up more of the page. Commonly you may have double line spacing, which is text on every second line.