I've heard it's a common practice for MMO developers to employ bots before the initial user base develops because it's hard to convince people to play your game when there's no one else playing it
also, there's a bunch of these .io games that are completely single-player (you play with AI) even though they look like multiplayer games because games are more exciting when it seems like there's someone on the other side of the screen
I wouldn't be surprised if Reddit, Twitter and similar sites employed bots to stir up interactions, to provide upcummies to normies to keep them addicted
paid trolls are also an obvious one, I've seen job offers about writing fake reviews, shilling products or companies on social media etc. NGOs surely employ similar tactics