Some people would just because they think that 175lbs is small to weigh.
200 at 15% to 175% at 3% would be the same amount of muscle. Which would you choose from the two?
i think most rational people would pick the lower bodyfat if the amount of muscle is the same.
you can build a hierarchy in terms of what aspect of bodybuilding is the easiest. putting on fat is the easiest, losing fat is the second easiest, losing fat while holding onto muscle is the second hardest, adding muscle without adding fat is the hardest.
someone 175 at 3% bf could easily pig out and shoot to 200 without risking an ounce of lost muscle tissue (i'd ever say it'd be impossible to do so without ADDING muscle). but that guy at 200 @ 15% will have a much harder time trimming down while maintaining muscle.