I always harvest the yeast and wash and sanitize the container - but I collect and repitch multiple times, so I don't want a whole slurry in there. I overpitched a light ale once and it was highly estery with US-05 slurry. I seem to recall that if the yeast don't reproduce sufficiently, they instead throw off acetaldehydes or phenols, because their full reproduction cycle has been short circuited. I will defer to the science guys on that, but it makes sense to at least remove half of the yeast cake if repitching to a comparable or smaller beer.
Definitely THE Science Guy!