Other than the short par 4, its the only type of hole that will often give you the strategic option of how to play the hole in terms of number of strokes you plan on reaching the goal given perfect execution.
And the par 5, by making you think an additional stroke ahead, has some advantages over the par 4 even considering that.
Sure, you could always label a 530 yard hole a par 4 (or hell, Kapalua's reachable 650 yard 18th?), but that's a seperate question entirely.