Mass Content Poster?

I see some people on this forum running dozens of child/slave accounts, which is pretty mindblowing. Do you have to handpick every image you want to be posted and schedule them with a bot, or is there a way to automate posting pictures within your niche every so often, such as running a scraper for certain hashtags or reposting images from a specific user? Or is it not even necessary to post content on child-slave accounts?