Also, if you always leave it down and there's a nighttime emergency crapping to be done, you won't have to fiddle with the light. Now I know, it's not like that happens often, but really, it only takes one bad shrimp or too much mexican food to learn you.
What I used to fight about with my past live in girlfriends was why do you feel the need to put the lid down? I mean you flushed right? so it shouldn't be gross in there. if you close the lid every time then every time you have to open it again. what's the point in that?