No, I didn't say not to reuse, just not to rinse. I reuse. I've repitched up to 25 generations. Could go longer.
What is important is good sanitation and not rinsing. Replacing the beer the yeast made with water raises the pH, removing important protection against infection. It also subjects yeast to damaging osmotic shock. Further, it introduces oxygen. This signals yeast to start its life cycle. It will consume the reserves it built up before dormancy, but finding no food to consume, may starve; and it will not have the needed reserves when it finally does get pitched into wort, and will be unprepared for a normal, healthy, and ordered fermentation. Culture yeast is dependent on a predictable cycle provided by us, the human brewers who've shaped it by selection. It expects to be oxygenated, fed wort, reproduce, build up reserves, and then rest waiting for the start of the next cycle to be signalled. It has lost the genes that allow for adaptability. On the other hand, wild yeast and bacteria retain the ability to quickly seize any opportunity at any time and jump to a different part of their metabolic cycle whenever there is available food. So disruption of the culture yeast's life cycle renders it unable to outcompete potential infecting organisms. All in all, rinsing presents various means to weaken yeast, and favor competing organisms. Over multiple generations the cumulative effects are increasingly devastating, but even in one fermentation cycle, there is no advantage and to rinsing and it will only lead to a weaker and less ordered fermentation.
Reuse yeast, definitely. Yeast generally take at least 3 generations to fully adapt from lab to actual brewery conditions and start performing at their best. Ensure good sanitation, store yeast under the beer it made, and directly repitch slurry without rinsing (rouse in a starter if necessary,) and you'll have better performance than starting with a new pack every time. If for some reason you do feel it is necessary to rinse to remove excessive trub, do it right at pitching time, when yeast needs oxygenation anyway. But I still feel it is just as effective to simply estimate a larger volume of slurry to make up for non yeast material mixed in.