Ronin is referring to the XHTML 2 spec. I was going to mention this, as it makes individual lines separate elements. Why? Because they can then be styled individually. Say you wanted the first line of every paragraph bold, then it could be done. Or the second line blue, the third line red and the fourth line green.
A nice colour fade would look great, from red to slightly darker red, with each line darkening a bit. To do that in HTML 4 would require spans and breaks I guess. Or even divs.