They’re indistinguishable because they’re copied from top-voted posts that are a few years old (title, text, and image if applicable). It’s guaranteed to produce a post that fits the community and gets a lot of engagement, so it’s a cheap and effective way to mature a bot account. Once you start looking for it, it’s everywhere, and Reddit admins don’t care.
I’m speculating, but my guesses are:
Once mature, it’s usually used for spam or astroturfing. There is a noticeable uptick around big elections, wars, etc.
I saw one repost-bot that metastisized into the most vile porn-spam-bot you can imagine, but they’re usually more subtle than that.