By restricting the allowable ingredients, it led to the extinction of many brewing traditions and local beer specialties, such as North German spiced beer and cherry beer, and led to the domination of the German beer market by pilsener style beers.

Which, I realize, ties back into the evening in a couple of different ways. North German Kirschenbier appears (according to the Intarweb, and reasonably enough) to have been part of the same tradition that produced Belgian Kriek, and the ban may have been the reason for the development of the Berliner Weiss, to substitute for the newly unavailable fruit beers.

(There are apparently some German brewpubs flouting the Reinheitsgebot now that EU law has superseded it, brewing with cherries, honey, and other previously verboten ingredients.)