I’m speculating, but my guesses are:

• Gathering enough karma to post on subreddits that have a minimum threshold.
• Getting enough post and comment history to pass a casual inspection, either by human moderators or spam filters.
• Maturing the account to the point where it can be sold to another shady company.
• Generally having a lot of bot accounts ready, just in case.

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.

Advertising or scams usually. A high amount of posts, comments, and karma makes an account look trustworthy.