Sorry for seeming clueless, but I am clueless. I've only brewed about 15 batches, or less, of extract beers. Thus far, I've always bought prepackaged recipe "kits" similar to a Betty Croker cake mix. Since finding this site, I am seeing a lot of questions regarding washing, rinsing and reusing yeast, but I havent seen (found) a reason why you wold? Is it just economical?