The only obvious world application for this would be to skew opinion one way or another by vastly spamming opinions that align with the bot operator.
Reviews of your movie overwhelmingly bad?
We can 'fix' that.
This is already being done, but fake reviews can usually be fairly easily spotted. If 'positive' reviews would be longer and somewhat coherent, they'd be much harder to spot.
Don't like 'The last Jedi'? Looks like you're no longer part of the majority.