The Solver precision parameter has direct influence on the speed and quality of the simulation. Lower values produce a more precise, although also slower, simulations. Here is a quick example:
Here is the animation.
The simulation time for the first (left) case is 41.7s, for the middle one - 42.9s, and for the last (right) one - 1m 4.9s.
Notice how the cloth flickers in the first case, because the precision is not enough. The last simulation is very smooth, and also slowest of all.
The precision also influences collision resolution. High values for the precision may cause intersections to occur in situations where lower values work properly.