It’s mentioned in this really good Verge article about SEO. I don’t think it’s a good sign for Reddit to just allow such blatant spam and makes me think how much subtler spam is out there too.
I’ve personally noticed more a few times in old threads you’ll find a comment made months later that’s recommending a product.
Oh it results in removal alright. It results in the removal of my legitimate account from the site due to “report abuse” because I reported those obvious bot farms incessantly.
Reddit admins implicitly encourage this sort of bot spam because any kind of Reddit activity shows active users, which means more displayed ads, which means money for Reddit. They do not give one flying fuck about actually reducing spam.