By extension, high-karma accounts that are run by marketing companies can post in a niche subreddit to subtly promote their product or disparage their competition, and they'll end up on the front page of that subreddit. They'll get a lot of views and a lot more engagement than the average unsophisticated user's post would -- and those astroturfed posts would, on average, rank higher in searches.

This is analogous to SEO, but rather more insidious and sneaky. You can spot SEO blogspam from a mile away. You don't know if a Reddit user is a real person, a bot, or a company's representative.

Reddit bots are used for upvote manipulation of legitimate posts by brand ambassadors/etc. The post histories are just to make the bot look legitimate.

I always assumed the botted accounts on Reddit were in the hands of marketing companies, ready to upvote posts saying "My Brand X headphones sound great" or "I changed from Brand Y to Brand Z cigarettes because the smooth taste never leaves me feeling over-smoked" or "I made big gains by putting my life savings into this sketchy investment" or whatever they're being paid to promote at the time.

I'd wager you could do a lot to influence public opinion with just an upvote ring, without the botted accounts actually needing to post messages.