Why wash a precipitate with ethanol after precipitation reaction?

PbI2 is slightly soluble (only 0.044g.100cc) in cold water but is insoluble in ethanol. NaNO3 is soluble in cold water, approx. 10g/100cc, but completely soluble in ethanol. So you will have less of a chance of rinsing some of your precipitate into the drain. I think it probably doesn't have a measurable effect, after all the reaction does use a water solution in the first place. But, if you are being extra careful.......