I started over 50 FPS on the iPhone, but now I'm bellow 30 PFS, I've seen most iPhone games clamped to either 60 or 30 FPS, even when 24 or less would give the illusion of movement.

I've concidered my limit to be a little bit over 15 FPS, in fact my physics simulation is updated at that rate (15.84 steps/s) as that is the lowest that still give fluid movement, a bit lower gives jerky motion.

Is there a practical reason why to clamp FPS way above the lower limit?

Update:

The following image could help to clarify

I can independently set the physic simulation step, frame rate, and simulation interval update.

My concern is why should I clamp any of those to values greater than the minimum?

For instance to conserve battery life I could just to choose the lower limits, but it seems that 60 or 30 FPS are the most used values.