>>26
screen.draw(bez);
is probably preferable to
screen.draw(x1, y1, xMid, yMid, x2, y2, rColor, gColor, bColor);
or whatever you're saying might be more efficient. Not only is the abstraction more coherent (drawing a curve vs drawing three points and three color components), you're also only copying a pointer versus putting all that jazz on the stack.
Of course, the question of "efficiency" in such a context is very likely moot anyhow. The overhead of the function call is likely to be dwarfed by the time spent computing the curve.