The requisite one urinal minimum you put between you and any other
men who
may be pissing at a row of urinals. It's a courtesy thing, and it's about proximity more than
line of sight: shame shields don't obviate the need for a buffer urinal.
Of course, when you're in a situation where the buffer is impossible because there are more
men than there are urinals (sporting events, concerts, etc.), the buffer urinal no longer applies.