In the old time days (1940's & '50/60's) the original AAU Mr. America contest had some judging outdoors (daylight) and as well as under the stage posing lights (of course). Wanted to get a better impression of a BB'er in natural and stage lighting. A complete muscle relaxed position, while in the lineup, was also required under both conditions. Both the natural light and muscles relaxed can give a better judgment of any physical flaws there may be. Some guy's are just born with better skin tone and can look outstanding in any sort of lighting (why the heavy tan or body makeup applied so much). But when relaxed and unflexed a better picture of the body's overall condition can be noted.
Side Bar: back in those old days of the Mr America, the contestants also had to do a few athletic move. Usually one of the Olympic lifts. They also had a sit down interview. About how they would represent the MR America title if they won it that year. Also about their speaking abilities and how they handled themselves. (rumor had it that the reason the Harold Poole lose the title was of his stutter..true or not, I don't know)